CCNA Study Guide

2006-05-24T14:20:00.000+08:00

2006-05-20T11:56:00.000+08:00

Best CCNA exam resources:

www.actualtests.com -Best resource so far(email me at certboy@gmail.com for more details)

2006-04-04T15:52:00.000+08:00

Configuring VLANs

Before you begin creating VLANs, you should determine whether the switch will participate in a VTP domain that will synchronize VLAN configuration with the rest of the network. You must also enable a trunk connection if you want to use VLANs across multiple switches.

The steps to configure a VLAN are:

Enable VTP (optional)
Enable Trunking (optional)
Create VLANs
Assign VLANs to ports

Verifying VLANs

Verifying the VLAN Configuration
Verifying VLAN Membership
Prevent VLANs from Crossing a Trunk Link
Prevent Individual VLANs from Crossing a Trunk Link
Verifying Trunk Links
Verifying VTP Information
Enabling VTP Pruning

Enable VTP

When adding a new switch to an existing domain, it is a good idea to add it in VTP client mode. This will prevent the switch from propagating any incorrect VLAN information to other switches. In this example we will setup a new VTP domain and place the switch into server mode. The password puts VTP into secure mode. Every switch in the management domain must have a password assigned to it for the management domain to function properly in secure mode.

   Switch1#configure terminal
Enter configuration commands, one per line. End with CNTL/Z
Switch1(config)#vtp server
Switch1(config)#vtp domain ciscotest
Switch1(config)#vtp password ccna

Enable Trunking

The next step is to create a trunk connection with the other switches that will be sharing VLAN information. To enable trunking on a port, enter interface configuration mode for the desired port, and then use the trunk command with the appropriate option:

   Switch1#configure terminal
Switch1(config)#interface f 0/26
Switch1(config-if)#trunk on

**`trunk` Command Options**
Option	Function
`on`	Puts the port into permanent trunking mode and negotiates to convert the link into a trunk link. The port becomes a trunk port even if the neighboring port does not agree to the change.
`off`	Puts the port into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. The port becomes a nontrunk port even if the neighboring port does not agree to the change.
`desirable`	Makes the port actively attempt to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on, desirable, or auto mode.
`auto`	Makes the port willing to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on or desirable mode. This is the default mode.
`negotiate`	Puts the port into permanent trunking mode but prevents the port from generating DTP frames. You must configure the neighboring port manually as a trunk port to establish a trunk link.

Create VLANs

To create a VLAN, enter global configuration mode and use the vlan command with the VLAN identifier (1-1005) and its name.

   Switch1#configure terminal
Switch1(config)#vlan 5 name accounting
Switch1(config)#vlan 6 name management

Assign VLANs to Ports

Now that the VLAN has been created, you can statically assign which ports will be members of the VLAN. A port can only belong to one VLAN at a time and by default, all ports are members of VLAN 1. To assign a VLAN to a port, enter interface configuration mode for the port and use the vlan-membership command.

   Switch1#configure terminal
Switch1(config)#interface e0/4
Switch1(config-if)#vlan-membership static 5
Switch1(config)#interface e0/5
Switch1(config-if)#vlan-membership static 5
Switch1(config)#interface e0/6
Switch1(config-if)#vlan-membership static 6

Verifying the VLAN Configuration

To view the VLANs configured on the switch, use the show vlan command.


Switch1#show vlan

VLAN    Name               Status            Ports
--------------------------------------------------
1       default            Enabled           1-3, 7-24, AUI, A, B
5       accounting         Enabled           4, 5
6       management         Enabled           6

Optionally you can view an individual VLAN to see how it's configured by using the show vlan [#] command.


Switch1#show vlan 5

VLAN  Name          Status      Ports
-------------------------------------
5     accounting    Enabled     2
-------------------------------------

VLAN  Type   SAID   MTU   Parent  RingNo BridgeNo Stp  Trans1 Trans2
---------------------------------------------------------------------
5  Ethernet 100005  1500   0        1       1     Unkn   0     0

Verifying VLAN Membership

To view which ports are assigned to a VLAN, use the following command:

   Switch1#show vlan-membership
   Port  VLAN   Membership
   1        1      Static
   2        1      Static
   3        1      Static
   4        5      Static
   5        5      Static
   6        6      Static
   7        1      Static
   8        1      Static    
      [Output Cut]

Prevent VLANs from Crossing a Trunk

All VLANs are configured on a trunked link unless you clear it manually. Use the following command if you don't want a trunk to carry VLAN information:

   Switch1(config)#int f0/26
Switch1(config-if)#clear trunk

Prevent Individual VLANs from Crossing a Trunk Link

You can clear individual VLANs from crossing a trunk link by using the following command:

   Switch1(config)#int f0/26
Switch1(config-if)#no trunk-vlan 5

Verifying Trunk Link

To verify a trunk port use the show trunk [a|b] command. The a is for port f0/26 while b represents f0/27.

   Switch1#show trunk a
DISL state:  Auto, Trunking: On, Encapsulation type:ISL

Switch1#show trunk allowed-vlans
1-4, 6-1004

Verifying VTP Information

After VTP has been enabled and configured, you can view the configuration with the following command:

   Switch1#show vtp
VTP Version                     : 2
Configuration Revision          : 2
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 2
VTP Operating Mode              : Server
VTP Password                    : ccna
VTP Domain Name                 : ciscotest
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Enabled
MD5 digest                      : 0xB9 0xC7 0x8D 0xB3 0xD4 0xBA 0x94 0x03
Configuration last modified by 192.168.1.86 at 7-25-01 01:22:24

Enabling VTP Pruning

If you enable VTP pruning on a VTP server, you will enable it for the entire domain. Enable VTP pruning with the following command:

   Switch1(config)#vtp pruning enable

Disable VTP pruning with:

   Switch1(config)#vtp pruning disable

2006-04-04T15:48:00.000+08:00

Virtual Local Area Networks

A virtual LAN (VLAN) is a group of hosts or network devices, such as routers (running transparent bridging) and bridges, that forms a single bridging domain. There can be several VLANs defined on a single switch. A VLAN can also span multiple switches. Using layer 2 protocols such as IEEE 802.1q and ISL (Inter-Switch Link) allow a VLAN to span across multiple switches. VLANs are formed to group related users together regardless of the physical connections of their hosts to the network. The users can be spread across a campus network or even across geographically isolated locations. Users can be organized into separate VLANs according to their department, location, function, application, address (logical or physical), or protocol used. The goal with VLANs is to group users into separate VLANs so their traffic will stay within the VLAN. When you configure VLANs, the network can take advantage of the following benefits:

Benefits of using VLANs

Broadcast Control - Just as switches physically isolate collision domains for attached hosts and only forward traffic out a particular port, VLANs refine this concept further and provide complete isolation between VLANs. A VLAN is a bridging domain, and all broadcast and multicast traffic is contained within it.
Security - VLANs provide security in two ways:
- High-security users can be grouped into a VLAN, possibly on the same physical segment, and no users outside of that VLAN can communicate with them.
- Because VLANs are logical groups that behave like physically separate entities, inter-VLAN communication can only be achieved through a router. When inter-VLAN communication occurs through a router, all the security and filtering functionality that routers traditionally provide can be used. In the case of nonroutable protocols, there can be no inter-VLAN communication. All communication must occur within the same VLAN.
Performance - You can isolate users that require high performance networks for bandwidth intensive projects, VLANs can isolate them and the rest of the network from each other.
Network Management - Software on the switch allows you to assign users to VLANs and, later, reassign them to another VLAN. Recabling to change connectivity is no longer necessary in the switched LAN environment because network management tools allow you to reconfigure the LAN logically in seconds.

Routers by default only send broadcasts within the originating network, but switches forward them to all segments. This is known as a flat network because it's one big broadcast domain. Switches and VLANs are used to replace the flat network. All members of a VLAN are in the same broadcast domain and receive all broadcasts. By default the broadcasts are filtered from all ports on a switch that aren't in the same VLAN. Routers, layer 3 switches, or Route Switch Modules (RSM) must be used in conjunction with switches to provide connections between networks (VLANs), which can stop broadcasts from propagating throughout the entire internetwork.

VLAN Organizations

A traditional collapsed backbone consists of a router with separate networks attached to its interfaces. Each node attached to the physical network need to have the same network number in order to communicate on the internetwork. On switches you can group users into communities of interest called VLAN Organizations. In a VLAN, network nodes of each VLAN can communicate with other nodes in the same VLAN, the nodes in one VLAN need to go through a router or other layer 3 device in order to communicate with other VLANs.

VLAN Memberships

VLANs are usually created by administrators who assign switch ports to VLANs. These are called static VLANs. Dynamic VLANs are configured by assigning all the host devices' hardware addresses into a database.

Static VLAN

Static VLANs are the typical method of creating VLANs and are the most secure. The switch port you assign a VLAN association to always maintains that association until an administrator changes the port assignment.

Dynamic VLAN

Dynamic VLANs determine a node's VLAN assignment automatically. Using intelligent management software, you can enable MAC addresses, protocols, or even applications to create dynamic VLANs. For example, if the MAC address is in a centralized database, and if it connects to a switch port, the VLAN management database can lookup the address and configure the port for the correct VLAN. If the user moves, the switch will automatically assign them to their correct VLAN.

Links in a Switched Environment

VLANs can span multiple connected switches by using frame tagging and trunk connections. Switches in the switch fabric must keep track of frames and which VLAN the frame belongs to. Frame tagging performs this function. Switches can then direct frames to the appropriate port.

Frame Tagging

Switches use frame tagging to keep track of users and frames as they travel the switch fabric and VLANs. Switch fabric is a group of connected switches. Frame tagging assigns a unique user-defined ID to each frame, also called VLAN ID or color. Frame tagging is to be used when an Ethernet frame traverses a trunked link. Each switch the frame traverses must identify the VLAN ID and then determine what to do with the frame based on its filter table. Once the frame reaches the exit to the access link, the VLAN ID is removed and the end device receives the frame without having to understand the VLAN ID. A VLAN interface can have only one VLAN ID, and VLAN trunk interfaces support multiple VLANs across them.

There are two types of links:
Access Links

Links that are only part of one VLAN are referred to as the native VLAN of the port. Any device attached to an access link is unaware of a VLAN membership. This device just assumes that it is part of a broadcast domain, without any understanding of the physical network. Switches remove any VLAN information before it is sent to an access link device. Access link devices can't communicate with any devices outside their VLAN without a router or layer 3 device.

Trunk Links

Trunks can carry multiple VLANs and are used to connect switches to other switches, to routers, or servers. Trunk links are only supported on Fast or Gigabit Ethernet (100 or 1000Mbps). Cisco switches support two ways to identify which VLAN a frame belongs to: ISL and 802.1q. If no trunk encapsulation type is specified when configuring an Ethernet trunk, ISL is used as the default. Trunk links have a native or default VLAN that is used if the trunk link fails. Trunked links carry the traffic of multiple VLANs from 1 to 1005 at a time. Trunking allows you to make a single port a part of multiple VLANs, so you can be in more than one broadcast domain at a time. When connecting switches together, trunk links can carry some or all VLAN information across the link. If you don't trunk the links then the switch will only carry VLAN 1 information across the link. Cisco switches use the Dynamic Trunking Protocol (DTP) to manage trunks. DTP is a PPP that was created to send trunk information across 802.1q trunks.

Trunking Methods

Inter-Switch Link - ISL is a Cisco proprietary protocol for interconnecting multiple switches and maintaining VLAN information as traffic goes between switches. ISL is similar to 802.10 as they both multiplex bridge groups over a high-speed backbone (ISL runs only on Fast Ethernet). With ISL, an Ethernet frame is encapsulated with a header that maintains VLAN IDs between switches. A 26-byte header that contains a 10-bit VLAN ID is prepended to the Ethernet frame. A VLAN ID is added to the frame only when the frame is destined for a non-local network. Since the frame is encapsulated, only devices running ISL can read it. If you need a protocol for other than Cisco Switches use 802.1q. ISL frames can be up to 1522 bytes long. On multi-VLAN ports, each frame is tagged as it enters the switch. ISL NICs allow servers to send and receive frames tagged with multiple VLANs so the frames can traverse multiple VLANs without going through a router. The ISL protocol can allow a file server to exist in multiple VLANs at the same time. Note that ISL encapsulation is only added to frames that are forwarded on a trunk link, and when they arrive at the access link the encapsulation is removed and the frame is delivered.
IEEE 802.1q - Created by the IEEE as a standard method of frame tagging. It actually inserts a field into the frame to identify the VLAN. If you are trunking between a Cisco switch and a non-Cisco switch, you will need to use 802.1q for the trunk to work.
IEEE 802.10 - Defines a method for securing bridging of data across a shared MAN (Metropolitan Area Network) backbone. The coloring (VLAN ID) of traffic across the FDDI backbone is achieved by inserting a 16-byte header between the source MAC and the Link Service Access Point (LSAP) of frames leaving a switch. This header contains the 4-byte VLAN ID or "color". The receiving switch removes the header and forwards the frame to interfaces that match the VLAN color.

Communicating between VLANs

To communicate between VLANs you need to have a router with an interface for each VLAN or a router that supports ISL routing. The lowest Cisco router that supports ISL routing is the 2600 series. If you're using a router with one interface and ISL, the interface should be at least 100Mbps (Fast Ethernet).

VLAN Trunking Protocol (VTP)

VTP is a protocol used between switches to simplify the management of VLANs. With VTP, you can make configuration changes centrally on a single Catalyst series switch and have those changes automatically communicated to all the other switches in the network.

VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs on a network-wide basis. VTP minimizes misconfigurations and configuration inconsistencies that can result in a number of problems, such as duplicate VLAN names, incorrect VLAN-type specifications, and security violations.

Developed by Cisco, it is the industry's first protocol implementation specifically designed for large VLAN deployments. VTP enhances VLAN deployment by providing the following:

Integration of ISL, 802.10, and ATM LAN-based VLANs.
Auto-intelligence within the switches for configuring VLANs.
Configuration consistency across the network.
An auto-mapping scheme for going across mixed-media backbones.
Accurate tracking and monitoring of VLANs.
Dynamic reporting of added VLANs across the network.
Plug-and-Play setup and configuration when adding new VLANs.

To allow VTP to manage your VLANs across the network, you must first create a VTP server. All servers that need to share VLAN information must use the same domain name, and a switch can only be in one domain at a time. If all your switches are in the same VLAN then you don't need to use VTP. VTP information is sent via a trunk port. Switches advertise VTP management domain information, as well as configuration revision number and all known VLANs with any specific parameters. Switches detect the additional VLANs within a VTP advertisement and then prepare to receive information on their trunk ports. The information would be VLAN ID, 802.10 SAID fields, or LANE information. Updates are sent out as revision numbers that are notification +1. Anytime a switch sees a higher revision number, it knows the information is newer and overwrites the database with the newer one.

Three modes of operation within a VTP

Server - Default mode for all catalyst switches. You need at least one to propagate VLAN data throughout the domain. The switch must be in server mode to create, add, or delete VLANs in a VTP domain. Any changes made while in server mode will be advertised to the entire VTP domain. Advertisements are sent every 5 minutes or whenever there is a change.
Client - Receives information from VTP servers and sends and receives updates, but can't make any changes. To add a switch to a VLAN, first make it a client to update the database, then change it to a server to make the changes and have them advertised or alternatively delete the VTP database with the delete vtp privileged EXEC mode command.
Transparent - Doesn't participate in the VTP domain, but will still forward VTP advertisements through the configured trunk links. Can add and create VLANs as it doesn't share its database with any other switch and changes made to its database are only considered locally significant.

VTP Advertisements

Each switch in the VTP domain sends periodic advertisements out each trunk port to a reserved multicast address. VTP advertisements are received by neighboring switches, which update their VTP and VLAN configurations as necessary.

The following global configuration information is distributed in VTP advertisements:

VLAN IDs (ISL and 802.1Q)
Emulated LAN names (for ATM LANE)
802.10 SAID values (FDDI)
VTP domain name
VTP configuration revision number
VLAN configuration, including maximum transmission unit (MTU) size for each VLAN
Frame format

VTP Pruning

VTP pruning enhances network bandwidth use by reducing unnecessary flooded traffic, such as broadcast, multicast, unknown, and flooded unicast packets. VTP pruning increases available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to access the appropriate network devices. By default, VTP pruning is disabled. VTP pruning only sends broadcasts to trunk links that must have the information. Enabling VTP pruning on a VTP server enables pruning for the entire management domain. VTP pruning takes effect several seconds after you enable it. By default, VLANs 2 through 1000 are pruning-eligible. VTP pruning does not prune traffic from VLANs that are pruning-ineligible. VLAN 1 is always pruning-ineligible; traffic from VLAN 1 cannot be pruned. VLAN 1 can never prune because it is an administrative VLAN.

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Configuring a Catalyst 1900 Switch

This page covers configuring a Cisco Catalyst 1900 Switch from the command line interface. This is the method that is tested on the CCNA 2.0 test, but you should know that you can also configure the switch from a Menu (runs on the command line) or you can use the Web interface (set the IP address on the Switch and enter the IP address in a web browser on a client to access the Switch's configuration web pages).

Setting Hostname, IP Address, and DFGW

You set these items the same way as for a router. The exception is that the IP address is for the entire device as opposed to a router, which has addresses for each interface. You should also know that you can telnet to a switch but you can't telnet from it.

   > enable
  # conf t
  Enter configuration commands, one per line.  End with CNTL/Z.
  (config)# hostname Switch1
  Swicth1(config)# ip address 192.168.1.75 255.255.255.224
  Switch1(config)# ip default-gateway 192.168.1.65
  Switch1(config)# ip domain-name foo.org

Viewing the IP Information

Use the show ip user Exec command to display global Internet Protocol (IP) configuration information.

   Switch1# show ip

  IP Address:192.168.1.75
  Subnet Mask:255.255.255.224
  Default Gateway:192.168.1.65
  Management VLAN: 1
  Domain name: foo.org
  Name server 1:192.168.1.70
  Name server 2:0.0.0.0
  HTTP server :Enabled
  HTTP port : 80
  RIP :Enabled

Setting Passwords

Use the enable password <1-15> <password> global configuration command to set unencrypted user Exec or privileged Exec passwords. Level 1-14 is for user Exec privileges while Level 15 is for privileged Exec privileges. The Password is a noncase-sensitive string of between 4 and 8 characters, spaces, and punctuation (except double quotes). Password strings with blank spaces must be enclosed in double quotes.

   Switch1(config)# enable password level 1 "CcNa 2.0"
  Switch1(config)# enable password level 15 CiScO123

Enable Secret Password

Use the enable secret global configuration command to set encrypted user Exec or privileged Exec passwords. The enable secret password is used in place of the enable password if it is set since the enable secret password is encrypted and therefore more secure.

   Switch1(config)# enable secret PaSs&oRd

Interfaces

Use the interface type slot/port global configuration command to choose an interface type and to enter interface configuration mode.

   Switch1(config)# interface ethernet 0/5
  Switch1(config-if)#

Setting the Interface Description

While in interface configuration mode you can use the description string command to set a description for an interface. The description can be from 1 to 80 alphanumeric characters. Use double quotes to enclose strings with spaces.

   Switch1(config-if)# description "Marketing VLAN"

Set the Port's Duplex

Use the duplex {auto | full | full-flow-control | half} interface configuration command to enable duplex mode for an interface.

Syntax Description:

`auto`	Auto-negotiation of duplex mode.
`full`	Full-duplex mode.
`full-flow-control`	Force full-duplex mode with flow control.
`half`	Half-duplex mode.

Example:

   Switch1(config-if)# duplex full

Show Version

This example shows how to display the switch hardware and firmware versions accessible from privileged Exec mode for the Catalyst 1900 switch.

   Switch1# show version

  Cisco Catalyst 1900/2820 Enterprise Edition Software
  Version V9.00.00(12)
  Copyright (c) Cisco Systems, Inc.  1993-1999
  Switch1 uptime is 2day(s) 22hour(s) 50minute(s) 21second(s)
  cisco Catalyst 1900 (486sxl) processor with 2048K/1024K bytes of memory
  Hardware board revision is 1
  Upgrade Status: No upgrade currently in progress.
  Config File Status: No configuration upload/download is in progress
  27 Fixed Ethernet/IEEE 802.3 interface(s)
  Base Ethernet Address: 00-E0-1E-7E-BE-80
  Switch1#

MAC Address Tables

Since layer 2 switches use MAC addresses to filter network traffic, it stands to reason that you can control MAC related functions. A Catalyst 1900 switch can store up to 1024 MAC addresses in its filter table. When the filter table is full, the switch will flood the network with all new incoming frames until one of the existing addresses in the table expires and is removed. To view the table of MAC addresses, use the following command:

   Switch1#show mac-address-table
  
  Number of permanent addresses :0
  Number of restricted static addresses :0
  Number of dynamic addresses :9

  Address           Dest Interface    Type         Source Interface List
  ----------------------------------------------------------------------------------
  00D0.5868.F583    FastEthernet 2    Dynamic      All
  00E0.1E74.6ADA    FastEthernet 1    Dynamic      All
  00E0.1E74.6AC0    FastEthernet 1    Dynamic      All
  0060.47D5.2770    FastEthernet 2    Dynamic      All
  00D0.5868.F580    FastEthernet 2    Dynamic      All
  00D0.5868.C8C0    FastEthernet 2    Dynamic      All
  00D0.5868.EF00    FastEthernet 2    Dynamic      All
  00E0.1E74.6080    FastEthernet 2    Dynamic      All
  00D0.C0F5.5B80    FastEthernet 2    Dynamic      All

Clearing the MAC Address Table

If clear mac-address-table is invoked with no options, all dynamic addresses are removed. If you specify an address but do not specify an interface, the address is deleted from all interfaces. If you specify an interface but do not specify an address, all addresses on the specified interface are removed.

   Switch1#clear mac-address-table

Setting Static MAC Addresses

Use the mac-address-table restricted static global configuration command to associate a restricted static address with a particular switched port interface (specified as type module/port). Use the no mac-address-table restricted static command to delete a restricted static address.

The following example shows how to configure a packet with MAC address of 0040.C80A.2F07 to come in on either Ethernet interface 1 or Ethernet interface 2 and be forwarded to the Fast Ethernet interface 27.

   Switch1(config)#mac-address-table restricted static 0040.C80A.2F07 f0/27 e0/1 e0/2

Setting Permanent MAC Addresses

Use the mac-address-table permanent global configuration command to associate a permanent unicast or multicast MAC address with a particular switched port interface (specified by type and module/port). Use the no mac-address-table permanent command to delete a permanent MAC address. This example shows how to specify that packets with the multicast destination address 0140.C80A.2F07 should be forwarded on the Fast Ethernet interface 27.

   Switch1(config)# mac-address-table permanent 0140.C80A.2F07 fastethernet 0/27

Using Port Security

Use the port secure interface configuration command to enable addressing security. Use the no port secure command to disable addressing security or to set the maximum number of addresses allowed on the interface to the default value. The default is 132, but can be from 1 to 132. The following example shows how to set the maximum MAC address count to 100 on the ethernet slot 0 port four interface.

   Switch# conf t
  Switch1(config)# interface ethernet 0/4
  Switch1(config-if)# port secure max-mac-count 100

Upgrading/ Restoring the IOS for a Catalyst 1900

You can upgrade or restore the IOS, but you can't back it up on Catalyst 1900 switches. To copy an IOS from a TFTP host use the following command.

Syntax:

   copy tftp://tftp_host's_address/IOS_filename opcode

Example:

   Switch1#copy tftp://192.168.1.70/cat1900EN_9_.bin opcode

Backing Up and Restoring the Catalyst 1900's Configuration

The configuration file is called nvram on a 1900 switch. To copy the file to a TFTP host, use the following command:

Syntax:

   copy nvram tftp://tftp_host's_address/config_name

Example:

   Switch1#copy nvram tftp://192.168.1.70/1900en

To restore the file from a TFTP host to the switch, use the following command:

Syntax:

   copy tftp://tftp_host's_address/config_name nvram

Example:

   Switch1#copy tftp://192.168.1.70/1900en nvram

Deleting the Startup-Configuration

To delete the startup-config (nvram), use the following command:

   Switch1#delete nvram

Change the LAN Switch Type

You can view the switch type with the privileged EXEC command show port system. To change the switch's switch type, use the following command:

   Switch1(config)#switching-type ?
  fragment-free       Fragment Free mode
  store-and-forward   Store-and-Forward mode
 
  Switch1(config)#switching-type store-and-forward

2006-04-04T15:43:00.000+08:00

Layer 2 Switching

Layer 2 switching is hardware based, it uses the host's Media Access Control (MAC) address.
Switches use Application Specific Integrated Circuits (ASIC) to build and maintain filter tables.
Switches tend to be faster than Routers, because they don't look at the logical address (Network layer headers), they instead use the hardware address defined at the Data Link (MAC) layer to decide whether to forward or discard the frame.
Layer 2 switching is so efficient because it doesn't modify the data packet only the frame encapsulating the packet; this also causes it to be less error prone.
Uses Layer 2 switching for network connectivity and network segmentation (each port is a separate collision domain).
Be careful how you segment your network, ensure that the users spend 80% of their time on their local segment, and all the segments of a switch are still in the same broadcast domain. Use routers to split up broadcast domains.

Benefits of LAN Switches (Layer 2 Services)

An individual Layer 2 switch might offer some or all of the following benefits:

Bandwidth---LAN switches provide excellent performance for individual users by allocating dedicated bandwidth to each switch port (for example, each network segment). This technique is known as microsegmenting.
VLANs---LAN switches can group individual ports into logical switched workgroups called VLANs, thereby restricting the broadcast domain to designated VLAN member ports. VLANs are also known as switched domains and autonomous switching domains. Communication between VLANs requires a router.
Automated packet recognition and translation---Cisco's unique Automatic Packet Recognition and Translation (APaRT) technology recognizes and converts a variety of Ethernet protocol formats into industry-standard CDDI/FDDI formats. With no changes needed in either client or server end stations the Catalyst solution can provide an easy migration to 100-Mbps server access while preserving the user's investment in existing shared 10Base-T LANs.

Three functions of layer 2 switching

Address learning - Layer 2 switches retain, in their filter tables, the source hardware address and port interface it was received on.
Forward/Filter decisions - When a frame is received, the switch looks at the destination hardware address and finds the interface it is on in the filter table. If the address is unknown, the frame is broadcast on all interfaces except the one it was received on.
Loop Avoidance - If multiple connections between switches exist for redundancy, network loops can occur. Spanning Tree Protocol is used to stop loops while still allowing redundancy.

Spanning Tree Protocol

STP is a Layer 2 link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path must exist at Layer 2 between two stations. STP operation is transparent to end stations, which do not detect whether they are connected to a single LAN segment or a switched LAN of multiple segments.

The Catalyst series switches use STP (IEEE 802.1D bridge protocol) on all Ethernet virtual LANS (VLANs). When you create fault-tolerant internetworks, you must have a loop-free path between all nodes in a network. In STP, an algorithm calculates the best loop-free path throughout a Catalyst-switched network. The switches send and receive spanning-tree packets at regular intervals (2 seconds). The switches do not forward the packets, but use the packets to identify a loop-free path. The default configuration has STP enabled for all VLANs.

Multiple active paths between stations cause loops in the network. If a loop exists in the network, you might receive duplicate messages. When loops occur, some switches see stations on both sides of the switch. This condition confuses the forwarding algorithm and allows duplicate frames to be forwarded.

To provide path redundancy, STP defines a tree that spans all switches in an extended network. STP forces certain redundant data paths into a standby (blocked) state. If one network segment in the STP becomes unreachable, or if STP costs change, the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating the standby path.

Defined as IEEE 802.1d
It first elects a root bridge (only 1 per network), root bridge ports are called designated ports which operate as forwarding-state ports. Forwarding-state ports can send and receive traffic. Other switches in your network are nonroot bridges.
The nonroot bridge's port with the fastest link to the root bridge is called the root port, and it sends and receives traffic.
Ports that have the lowest cost to the root bridge are called designated ports. The other ports on the bridge are considered non designated and will not send or receive traffic, (blocking mode).
Switches or bridges running STP, exchange information with what are called Bridge Protocol Data Units (BPDU). BPDUs send configuration information using multicast frames, BPDUs are also used to send the bridge ID of each device to other devices. The bridge ID is used to determine the root bridge in the network and to determine the root port. The Bridge ID is 8 bytes long, includes priority and MAC address. The default priority of devices using IEEE STP is 32,768 (2¹⁵).
To determine the root bridge the priority and the MAC addresses are combined, if priority is the same, the MAC address is used to determine the who has the lowest ID, which determines who will be the root bridge.
Path Cost is used to determine which ports will be used to communicate with the root bridge (designated ports). STP cost is the total accumulated path cost based on the bandwidth of the links. The slower the link the higher the cost.

Spanning Tree Protocol Port States

Blocking - doesn't forward any frames, but still listens to BPDUs. Ports default to blocking when the switch powers on. Used to prevent network loops. If a blocked port is to become the designated port, it will first enter listening state to ensure that it won't create a loop once it goes into forwarding state.
Listening - listens to BPDUs to ensure no loops occur on the network before passing data frames.
Learning - learns MAC addresses and builds filter table, doesn't forward frames.
Forwarding - sends and receives all data on the bridge ports. A forwarding port has been determined to have the lowest cost to the root bridge.

LAN Switching Modes

Store and Forward - the entire frame is copied into its buffer and computes the Cyclic Redundancy Check (CRC). Since it copies the entire frame, latency varies with frame length. If the frame has a CRC error, is too short (<64>1518 bytes) it is discarded. If no error, the destination address (MAC) is looked up in the filter table and is sent to the appropriate interface. Is the default state for 5000 series switches.
Cut Through - fastest switching mode as only the destination address is copied. It will then look up the address in its filter table and send the frame to the appropriate interface.
Fragment Free - modified form of Cut Through switching. The switch waits for the first 64 bytes to pass before forwarding the frame. If the packet has an error, it usually occurs in the first 64 bytes of the frame. Default mode for 1900 switches.

2006-04-04T09:14:00.000+08:00

LAN SWITCHING

Lan Switches

So, what are LAN switches? Switches are essentiallY mult-port bridges. Switches operate on the same basic principle as bridges. The difference is that essentially each host is often connected directly to a port on the switch, effectively resulting in each host having its own dedicated segment (microsegmentation). By examining MAC addresses the switch learns where hosts are located and forwards frames only to the necessary port. Because the decision to forward packets is based on layer 2 addresses, these types of switches are often called frame switches. Note: Some vendors also sell LAN switches that incorporate functions that operate on layer 3 information. Such switches are often referred to as multi-layer switches.

The benefits of switches are enormous. With Full-Duplex ethernet support, collisions can be virtually eliminated. Each host on the switch essentially has access to the full amount of available bandwidth.

There are two primary of Lan Switching modes, Store & Forward and Cut Through.

Store & Forward

This is the mode used by Catalyst 5000 series switches. In this mode an entire frame is read into a memory buffer on the switch. The frame is then analyzed for errors (CRC computation). If the frame is good, the switch consults its table of known MAC addresses and forwards the frame to the appropriate port. This method has the benefit of having each frame checked for errors and discarded if mal-formed. However, because it must read the entire frame into memory and peform the CRC, there is a higher degree of latency when compared to other methods.

Cut Through

This is an option in some EtherSwitch models. In Cut-Through switching, only the destination MAC address is read into memory. This is done simply to determine to which port to forward the frame. Once the destination port is known the switch immediatly begins forward the frame to that port. It does not do any error checking. The benefit of this method of switching is reduced latency but at the cost of potentially sending unwanted, mal-formed frames to host computers. Some cut-through switches attempt to reduce problems by filtering out collision fragments. Collision fragments are less than 64 bytes, so the switch reads 64bytes before beginning to forward the frame. Cisco refers to the standard cut-through switch as Fast Forward and those that filter collision fragments as Fragment Free.

Virtual LANs

Another great benefit of modern switches is a capability to created virtual LANs (VLANs). After a VLAN is established on a switch, frames (broadcast, multicast, or unicast) will only be forwarded to that particular VLAN. VLANs become particularly beneficial in their capability to span switches. No longer is the physical location of a host the determining factor in which LAN it belongs. This is accomplished by inserting a VLAN ID into the frame that identifies to which VLAN the frame belongs. This is used only in the switch framework and is removed before the final switch in a network forwards the frame to the destination port.

2006-04-04T09:02:00.000+08:00

MANAGING A CISCO INTERNETWORK

Cisco has TFTP server software that can be run on a computer.
Three places a router can look for a valid Cisco IOS - Flash, TFTP Server or ROM.
To copy the current config to a TFTP server type “copy running-config tftp”. To load a copy type “copy tftp run”.

Show memory is used to see how the system allocates memory for different purposes.

Show stacks monitors the stack use and if the reboot was the result of a system crash, and displays the last system reboot.

Show Buffers reveals the size of the buffers (S, M, Big, VeryBig, L, and Huge)

Show Flash describes the flash memory and the size of files and how much memory is free.

Cisco Discovery Protocol (CDP) – allows you access to configuration information on other routers with a single command. Running Subnetwork Access Protocol (SNAP) at the Data Link layer, two devices running different Network Layer protocols can still communicate. CDP runs by default on 10.3 versions and earlier. Once a router is found, it can display information about the upper-layer protocols. Find by typing “sh cdp int” will show interfaces configured to run CDP.

Telnet is a virtual terminal protocol.

“sh hosts” will show all the names of routers that your router knows about, assuming DNS is running on router or on a server. Router as a DNS server, use “ip domain-lookup, and “ip name-server ip_address”

You just received an output that states the CDP hold time, hardware, port ID, and local interface. What was the command you typed in?

“Show cdp neighbor” will show the hardware platform (Cisco 2500) the local interface the routers are connected through, the hold time, the port id of the remote router and the device id and its capability.

What’s the default CDP hold time in seconds?

180 - 3 times the default broadcast frequency, which is 60 seconds

What's the default CDP update broadcast rate for routers in seconds?

60 seconds. Changed with the cdp timer command.

What type of frame does CDP use to gather information about its directly connected neighbors?

CDP uses SNAP by default.

Which command do you type to view the hostnames configured in your router (choose two)?

Show hosts or sh host will show the ip host table configured on the router.

How can you view the CDP information received from all routers?

Show cdp entry or sh cdp entry * will show you entries of CDP information received from the neighbor routers.

If you want to type in the hostname Bob instead of the IP address 172.16.10.1 to access the remote router named Bob, what should you do?

“config t, ip host bob 172.16.10.1”.

If you type “copy tftp flash”, which event did you cause?

Copied a file from TFTP server to router flash. The router will look to a TFTP host for a valid Cisco IOS to copy into EEPROM, or Flash.

If you want to load a new Cisco IOS into your router's memory, which command should you use?

“copy tftp flash” tells the router to look to a TFTP server.

What does it mean if you’re running a trace and receive a “P” as a response?

Protocol unreachable

If you want to configure the router configuration stored in NVRAM, which command should you use?

“config mem” copies the startup-config into running-config.

Which command will load the Cisco router configuration into RAM (choose three)?

To reload the router, type “Reload” or “copy startup-config running-config”, or ”copy tftp running-config”.

What command will copy your router configuration to a TFTP server?

“copy star tftp” or “copy runn tftp”

What command should you use to have your router load the valid Cisco IOS from a TFTP server?

“boot system tftp ”

Which command will you use if you want to disable DNS lookup?

“no ip domain-lookup” will disable DNS.

Which command do you use to configure your router to do a domain-lookup?

IP name-server 10.10.10.10

After telneting into multiple routers simultaneously, what command can you type to see these connections?

“sh sessions” will show all that are open.

kNOW the password recovery processes for both 25xx and 26xx router

2006-03-30T08:36:00.000+08:00

CCNA REVISION QUESTION

Identify the true statements.

A. Ethernet is a broadcast media.

B. Ethernet is a non-broadcast media.

C. Ethernet does not allow a device to be given priority to transmit.

D. Ethernet allows a host to be given priority to transmit over other hosts on the same segment.

ANSWER: A & C

2006-03-30T08:32:00.000+08:00

CCNA REVISION QUESTION

What term is given to the point in an ISDN network where responsibility for the equipment goes from the customer to the telco?

A. DE

B. CE

C. DEMARC

D. DTE

E. R

F. S

G. T

ANSWER: C, DEMARC

2006-03-30T08:27:00.000+08:00

CCNA Revision Question (ROUTING PROTOCOLS)

The term "cost" refers to the metric of what routing protocol?

A. RIPv1

B. RIPv2

C. IGRP

D. OSPF

E. EIGRP

F. Static Routing

ANSWER : OSPF (D)

2006-03-28T13:42:00.000+08:00

ISDN (INTEGRATED SERVICES DIGITAL NETWORK)

ISDN

Integrated Services Digital Network

Terminal equipment types:

TE1: understands ISDN

TE2: predates ISDN and needs a TA (terminal adapter) to work

ISDN reference points:

R: between non-isdn device and TA

S: between terminal and NT2 device

T: point between NT1 and NT2

U: point between NT1 and carrier line termination device

ISDN protocol codes:

E: existing telephone network

I: concepts, terms, and services

Q: switching and signaling

ISDN service levels:

Connect to lines with SPIDs (service Profile Identfiers) (phone numbers..)

BRI: Basic Rate Interface: 2B + 1D

B = 64kbs, D=16Kbps = 128kbs plus control

PRI: Primary Rate Interface: 23B + 1D

Total of 1.544Mbps

Configuring ISDN BRI

#isdn switch-type ?

tons of proprietary switch types

#interface

typicaly bri0, or something like that.

#encap ppp

ppp is method used to setup isdn phone calls

#isdn spid1

#isdn spid2

2006-03-28T13:36:00.000+08:00

FRAME-RELAY

Frame Relay

Shared Bandwidth

Can setup a CIR (Committed Information Rate)

Assumed error-checking is handled at another, higher, layer

PVCs are created at layer 2.

DLCIs: Data-link connection Identifiers : are used to identify virtual circuit connections.

DLCI address are assigned by the provider and then mapped to IP addresses by the router

LMI: Local management Interface

These are autodetected in current IOS versions….. however:

Keyword Meaning

Cisco: defined by industry group, and default

ANSI: Annex D defined by T1.617

Q933a: Defined by ITU-T Annex A Q.933A

LMI can be used to determine the global significance of the DLCI numbers.

Setup of Frame Relay on Cisco

#interface

#encapsulation frame-relay [ietf, or default is cisco]

use default to talk to other cisco routers, use ietf encapsulation to talk to non-cisco.

#frame-relay interface-dlci

to map dlci number to current interface, or subinterface

Then specify an IP address for that subinterface

Optionally you can hard-code the address on the other end.

#encap frame-relay [ietf]

#no inverse-arp

turns off auto addressing features

#ip address

#frame-relay map ip

[cisco] [broadcast]

this lets you mix encap types, and allow broadcast over interface

Monitoring Frame Relay

#show frame ?

ip ip statistics

lmi lmi stats

map map table

pvc pvc stats – this one displays the DLCI #

route route info

traffic protocol stats

2006-03-23T16:33:00.000+08:00

PPP CONFIGURATION COMMANDS

Interface commands

Enable ppp on the interface encapsulation ppp

Enable authentication (chap pap) ppp authentication chap / pap

Global Commands

create a username and password for logging in username password

Show Commands

See encapsulation , open LCP's and more show interface serial 0

Debug Commands

View the authentication process debug ppp authentication

2006-03-23T14:52:00.000+08:00

WAN LINK OPTIONS

Circuit switching establishes a dedicated physical connection for voice or data between a sender and receiver. Before communication can start, it is necessary to establish the connection by setting the switches. This is done by the telephone system, using the dialed number. ISDN is used on digital lines as well as on voice-grade lines. If the local loop is not directly connected to the telephone system, a digital subscriber line (DSL) may be available.

To avoid the delays associated with setting up a connection, telephone service providers also offer permanent circuits. These dedicated or leased lines offer higher bandwidth than is available with a switched circuit. Examples of circuit-switched connections include:

Plain Old Telephone System (POTS)

ISDN Basic Rate Interface (BRI)

ISDN Primary Rate Interface (PRI)

Many WAN users do not make efficient use of the fixed bandwidth that is available with dedicated, switched, or permanent circuits, because the data flow fluctuates. Communications providers have data networks available to more appropriately service these users. In these networks, the data is transmitted in labeled cells, frames, or packets through a packet-switched network. Because the internal links between the switches are shared between many users, the costs of packet switching are lower than those of circuit switching. Delays (latency) and variability of delay (jitter) are greater in packet-switched than in circuit-switched networks. This is because the links are shared and packets must be entirely received at one switch before moving to the next. Despite the latency and jitter inherent in shared networks, modern technology allows satisfactory transport of voice and even video communications on these networks.

Packet-switched networks may establish routes through the switches for particular end-to-end connections. Routes established when the switches are started are PVCs. Routes established on demand are SVCs. If the routing is not pre-established and is worked out by each switch for each packet, the network is called connectionless.

To connect to a packet-switched network, a subscriber needs a local loop to the nearest location where the provider makes the service available. This is called the point-of-presence (POP) of the service. Normally this will be a dedicated leased line. This line will be much shorter than a leased line directly connected to the subscriber locations, and often carries several VCs. Since it is likely that not all the VCs will require maximum demand simultaneously, the capacity of the leased line can be smaller than the sum of the individual VCs. Examples of packet or cell switched connections include:

Frame Relay

X.25

ATM

2006-03-23T14:37:00.000+08:00

PACKET AND CIRCUIT SWITCHING

Packet-switched networks were developed to overcome the expense of public circuit-switched networks and to provide a more cost-effective WAN technology.

When a subscriber makes a telephone call, the dialed number is used to set switches in the exchanges along the route of the call so that there is a continuous circuit from the originating caller to that of the called party. Because of the switching operation used to establish the circuit, the telephone system is called a circuit-switched network. If the telephones are replaced with modems, then the switched circuit is able to carry computer data.

The internal path taken by the circuit between exchanges is shared by a number of conversations. Time division multiplexing (TDM) is used to give each conversation a share of the connection in turn. TDM assures that a fixed capacity connection is made available to the subscriber.

If the circuit carries computer data, the usage of this fixed capacity may not be efficient. For example, if the circuit is used to access the Internet, there will be a burst of activity on the circuit while a web page is transferred. This could be followed by no activity while the user reads the page and then another burst of activity while the next page is transferred. This variation in usage between none and maximum is typical of computer network traffic. Because the subscriber has sole use of the fixed capacity allocation, switched circuits are generally an expensive way of moving data.

An alternative is to allocate the capacity to the traffic only when it is needed, and share the available capacity between many users. With a circuit-switched connection, the data bits put on the circuit are automatically delivered to the far end because the circuit is already established. If the circuit is to be shared, there must be some mechanism to label the bits so that the system knows where to deliver them. It is difficult to label individual bits, therefore they are gathered into groups called cells, frames, or packets. The packet passes from exchange to exchange for delivery through the provider network. Networks that implement this system are called packet-switched networks.

The links that connect the switches in the provider network belong to an individual subscriber during data transfer, therefore many subscribers can share the link. Costs can be significantly lower than a dedicated circuit-switched connection. Data on packet-switched networks are subject to unpredictable delays when individual packets wait for other subscriber packets to be transmitted by a switch.

The switches in a packet-switched network determine, from addressing information in each packet, which link the packet must be sent on next. There are two approaches to this link determination, connectionless or connection-oriented. Connectionless systems, such as the Internet, carry full addressing information in each packet. Each switch must evaluate the address to determine where to send the packet. Connection-oriented systems predetermine the route for a packet, and each packet need only carry an identifier. In the case of Frame Relay, these are called Data Link Control Identifiers (DLCI). The switch determines the onward route by looking up the identifier in tables held in memory. The set of entries in the tables identifies a particular route or circuit through the system. If this circuit is only physically in existence while a packet is traveling through it, it is called a Virtual Circuit (VC).

The table entries that constitute a VC can be established by sending a connection request through the network. In this case the resulting circuit is called a Switched Virtual Circuit (SVC). Data that is to travel on SVCs must wait until the table entries have been set up. Once established, the SVC may be in operation for hours, days or weeks. Where a circuit is required to be always available, a Permanent Virtual Circuit (PVC) will be established. Table entries are loaded by the switches at boot time so the PVC is always available.

2006-03-23T14:33:00.000+08:00

WAN ENCAPSULATION

Data from the network layer is passed to the data link layer for delivery on a physical link, which is normally point-to-point on a WAN connection. The data link layer builds a frame around the network layer data so the necessary checks and controls can be applied. Each WAN connection type uses a Layer 2 protocol to encapsulate traffic while it is crossing the WAN link. To ensure that the correct encapsulation protocol is used, the Layer 2 encapsulation type used for each router serial interface must be configured. The choice of encapsulation protocols depends on the WAN technology and the equipment. Most framing is based on the HDLC standard.

HDLC framing gives reliable delivery of data over unreliable lines and includes signal mechanisms for flow and error control. The frame always starts and ends with an 8-bit flag field, the bit pattern 01111110. Because there is a likelihood that this pattern will occur in the actual data, the sending HDLC system always inserts a 0 bit after every five 1s in the data field, so in practice the flag sequence can only occur at the frame ends. The receiving system strips out the inserted bits. When frames are transmitted consecutively the end flag of the first frame is used as the start flag of the next frame.

The address field is not needed for WAN links, which are almost always point-to-point. The address field is still present and may be one or two bytes long. The control field indicates the frame type, which may be information, supervisory, or unnumbered:

Unnumbered frames carry line setup messages.

Information frames carry network layer data.

Supervisory frames control the flow of information frames and request data retransmission in the event of an error.

The control field is normally one byte, but will be two bytes for extended sliding windows systems. Together the address and control fields are called the frame header. The encapsulated data follows the control field. Then a frame check sequence (FCS) uses the cyclic redundancy check (CRC) mechanism to establish a two or four byte field.

Several data link protocols are used, including sub-sets and proprietary versions of HDLC. Both PPP and the Cisco version of HDLC have an extra field in the header to identify the network layer protocol of the encapsulated data.

2006-03-23T14:29:00.000+08:00

WAN STANDARDS

WANs use the OSI reference model, but focus mainly on Layer 1 and Layer 2. WAN standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation. WAN standards are defined and managed by a number of recognized authorities.

The physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections to the services provided by a communications service provider. Some of the common physical layer standards are listed in Figure , and their connectors illustrated in Figure .

The data link layer protocols define how data is encapsulated for transmission to remote sites, and the mechanisms for transferring the resulting frames. A variety of different technologies are used, such as ISDN, Frame Relay or Asynchronous Transfer Mode (ATM). These protocols use the same basic framing mechanism, high-level data link control (HDLC), an ISO standard, or one of its sub-sets or variants.

2006-03-23T14:25:00.000+08:00

WAN DEVICES

WANs are groups of LANs connected together with communications links from a service provider. Because the communications links cannot plug directly into the LAN, it is necessary to identify the various pieces of interfacing equipment.

LAN-based computers with data to transmit send data to a router that contains both LAN and WAN interfaces. The router will use the Layer 3 address information to deliver the data on the appropriate WAN interface. Routers are active and intelligent network devices and therefore can participate in network management. Routers manage networks by providing dynamic control over resources and supporting the tasks and goals for networks. Some of these goals are connectivity, reliable performance, management control, and flexibility.

The communications link needs signals in an appropriate format. For digital lines, a channel service unit (CSU) and a data service unit (DSU) are required. The two are often combined into a single piece of equipment, called the CSU/DSU. The CSU/DSU may also be built into the interface card in the router.

A modem is needed if the local loop is analog rather than digital. Modems transmit data over voice-grade telephone lines by modulating and demodulating the signal. The digital signals are superimposed on an analog voice signal that is modulated for transmission. The modulated signal can be heard as a series of whistles by turning on the internal modem speaker. At the receiving end the analog signals are returned to their digital form, or demodulated.

When ISDN is used as the communications link, all equipment attached to the ISDN bus must be ISDN-compatible. Compatibility is generally built into the computer interface for direct dial connections, or the router interface for LAN to WAN connections. Older equipment without an ISDN interface requires an ISDN terminal adapter (TA) for ISDN compatibility.

Communication servers concentrate dial-in user communication and remote access to a LAN. They may have a mixture of analog and digital (ISDN) interfaces and support hundreds of simultaneous users.

2006-03-23T14:24:00.000+08:00

WAN TECHNOLOGY

A WAN is a data communications network that operates beyond the geographic scope of a LAN. One primary difference between a WAN and a LAN is that a company or organization must subscribe to an outside WAN service provider in order to use WAN carrier network services. A WAN uses data links provided by carrier services to access the Internet and connect the locations of an organization to each other, to locations of other organizations, to external services, and to remote users. WANs generally carry a variety of traffic types, such as voice, data, and video. Telephone and data services are the most commonly used WAN services.

Devices on the subscriber premises are called customer premises equipment (CPE). The subscriber owns the CPE or leases the CPE from the service provider. A copper or fiber cable connects the CPE to the service provider’s nearest exchange or central office (CO). This cabling is often called the local loop, or "last-mile". A dialed call is connected locally to other local loops, or non-locally through a trunk to a primary center. It then goes to a sectional center and on to a regional or international carrier center as the call travels to its destination.

In order for the local loop to carry data, a device such as a modem is needed to prepare the data for transmission. Devices that put data on the local loop are called data circuit-terminating equipment, or data communications equipment (DCE). The customer devices that pass the data to the DCE are called data terminal equipment (DTE). The DCE primarily provides an interface for the DTE into the communication link on the WAN cloud. The DTE/DCE interface uses various physical layer protocols, such as High-Speed Serial Interface (HSSI) and V.35. These protocols establish the codes and electrical parameters the devices use to communicate with each other.

WAN links are provided at various speeds measured in bits per second (bps), kilobits per second (kbps or 1000 bps), megabits per second (Mbps or 1000 kbps) or gigabits per second (Gbps or 1000 Mbps). The bps values are generally full duplex. This means that an E1 line can carry 2 Mbps, or a T1 can carry 1.5 Mbps, in each direction simultaneously.

2006-03-23T14:18:00.000+08:00

WAN TECHNOLOGIES

As the enterprise grows beyond a single location, it is necessary to interconnect the LANs in the various branches to form a wide-area network (WAN). This module examines some of the options available for these interconnections, the hardware needed to implement them, and the terminology used to discuss them.

There are many options currently available today for implementing WAN solutions. They differ in technology, speed, and cost. Familiarity with these technologies is an important part of network design and evaluation.

If all data traffic in an enterprise is within a single building, a LAN meets the needs of the organization. Buildings can be interconnected with high-speed data links to form a campus LAN if data must flow between buildings on a single campus. However, a WAN is needed to carry data if it must be transferred between geographically separate locations. Individual remote access to the LAN and connection of the LAN to the Internet are separate study topics, and will not be considered here.

Most students will not have the opportunity to design a new WAN, but many will be involved in designing additions and upgrades to existing WANs, and will be able to apply the techniques learned in this module.

Students completing this module should be able to:

Differentiate between a LAN and WAN
Identify the devices used in a WAN
List WAN standards
Describe WAN encapsulation
Classify the various WAN link options
Differentiate between packet-switched and circuit-switched WAN technologies
Compare and contrast current WAN technologies
Describe equipment involved in the implementation of various WAN services
Recommend a WAN service to an organization based on its needs

2006-03-21T10:33:00.000+08:00

Revision Question on Subnetting - 2

1. You have a class C n/w and you need 10 subnets. You wish to have as many addresses available for hosts as possible. Which one of the following subnet masks should you use?

A. 255.255.255.192
B. 255.255.255.224
C. 255.255.255.240
D. 255.255.255.248
E. None of the above

ANSWER: C

2. How many subnetworks and hosts are available per subnet if you apply a /28 mask to the 210.10.2.0 class C n/w?

A. 30 N/WS and 6 hosts
B. 6 N/WS and 30 hosts
C. 8 N/Ws and 32 hosts
D. 32 N/Ws and 18 hosts
E. 14 N/Ws and 14 hosts
F. None of the above

ANSWER: E

2006-03-21T09:57:00.000+08:00

ACCESS-LISTS

Access lists are compared in the order of the lines, and only until a match was made. There is also an implicit deny at the end that the packet will be thrown out if there is no match. Usually want to place commonly matched lines at the top of the list. The list is created and then applied to a specific interface.

“access-list ”

1-99 IP Standard
100-199 IP Extended
200-299 Protocol type-code
300-399 DECNet

600-699 Appletalk
700-799 48-bit MAC address
800-899 IPX Standard
900-999 IPX Extended
1000-1099 IPX SAP
1100-1199 Extended 48-bit MAC
1200-1299 IPX Summary Address

“access-group ” Use group to apply the access-list to an interface. Only one access list is allowed in, and one outbound from the interface. Wildcard 0.0.0.255 will give access/deny access to all nodes in the range. Set to 0.0.0.0 will allow only that host.

In standard IP access lists, we can only compare with source address information.

In extended, we can limit via source address, destination address, protocol, and port information.

Clear access-list will clear the counters for the access list and start new.
Show ip access-list will show only IP based access lists.
Show IP interface e0 will show what access-list is applied to the interface.

IP standard access lists use which of the following as a basis for permitting or denying packets?
Source address

To specify all hosts in the class B IP network 172.16.0.0, which wildcard access list mask would you use?
0.0.255.255 The access list is the opposite of the IP. If you want all hosts on the subnet for Class B, you would enter 0.0.255.255. This accepts any address in the octet.

IP extended access lists use which of the following as a basis for permitting or denying packets?
Access list can look at the source and destination access lists when making filtering decisions, but can also filter by port and protocol.

Which of the following are valid ways to refer only to host 172.16.30.55 in an IP access list?
172.16.30.55 0.0.0.0 or host 172.16.30.55

Which of the following access lists will allow only WWW traffic into network 196.15.7.0?
Access-list 100 permit tcp any 196.15.7.0 0.0.0.255 eq www

Which of the following will show which ports have IP access lists applied?
Show ip interface and show running config

Which of the following are logged when IP access list logging is enabled?
Source address, source port, destination address, destination port, protocol, and access list number.

Which of the following commands will show an extended access list 187?
Sh ip access-list and sh access-list 187

What is the IP extended access list range?
100-199

Which of the following commands is valid for creating an extended IP access list?
Access-list 101 permit tcp host 172.16.30.0 any eq 21 log

What are three ways to monitor IP access lists?
Sh ip interface, sh run, and sh access-lists

2006-03-16T15:38:00.000+08:00

WHAT DOES NAT DO?

NAT is like the receptionist in a large office. Let's say you have left instructions with the receptionist not to forward any calls to you unless you request it. Later on, you call a potential client and leave a message for that client to call you back. You tell the receptionist that you are expecting a call from this client and to put her through.

The client calls the main number to your office, which is the only number the client knows. When the client tells the receptionist that she is looking for you, the receptionist checks a lookup table that matches your name with your extension. The receptionist knows that you requested this call, and therefore forwards the caller to your extension.

Developed by Cisco, Network Address Translation is used by a device (firewall, router or computer) that sits between an internal network and the rest of the world. NAT has many forms and can work in several ways:

Static NAT - Mapping an unregistered IP address to a registered IP address on a one-to-one basis. Particularly useful when a device needs to be accessible from outside the network.
In static NAT, the computer with the IP address of 192.168.32.10 will always translate to 213.18.123.110.

Dynamic NAT - Maps an unregistered IP address to a registered IP address from a group of registered IP addresses.
In dynamic NAT, the computer with the IP address 192.168.32.10 will translate to the first available address in the range from 213.18.123.100 to 213.18.123.150.
Overloading - A form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address by using different ports. This is known also as PAT (Port Address Translation), single address NAT or port-level multiplexed NAT.
In overloading, each computer on the private network is translated to the same IP address (213.18.123.100), but with a different port number assignment.

Overlapping - When the IP addresses used on your internal network are registered IP addresses in use on another network, the router must maintain a lookup table of these addresses so that it can intercept them and replace them with registered unique IP addresses. It is important to note that the NAT router must translate the "internal" addresses to registered unique addresses as well as translate the "external" registered addresses to addresses that are unique to the private network. This can be done either through static NAT or by using DNS and implementing dynamic NAT.
The internal IP range (237.16.32.xx) is also a registered range used by another network. Therefore, the router is translating the addresses to avoid a potential conflict with another network. It will also translate the registered global IP addresses back to the unregistered local IP addresses when information is sent to the internal network.
The internal network is usually a LAN (Local Area Network), commonly referred to as the stub domain. A stub domain is a LAN that uses IP addresses internally. Most of the network traffic in a stub domain is local, so it doesn't travel outside the internal network. A stub domain can include both registered and unregistered IP addresses. Of course, any computers that use unregistered IP addresses must use Network Address Translation to communicate with the rest of the world.
NAT can be configured in various ways. In the example below, the NAT router is configured to translate unregistered (inside, local) IP addresses, that reside on the private (inside) network, to registered IP addresses. This happens whenever a device on the inside with an unregistered address needs to communicate with the public (outside) network.

An ISP assigns a range of IP addresses to your company. The assigned block of addresses are registered, unique IP addresses and are called inside global addresses. Unregistered, private IP addresses are split into two groups. One is a small group (outside local addresses) that will be used by the NAT routers. The other, much larger group, known as inside local addresses, will be used on the stub domain. The outside local addresses are used to translate the unique IP addresses, known as outside global addresses, of devices on the public network.
IP addresses have different designations based on whether they are on the private network (stub domain) or on the public network (Internet), and whether the traffic is incoming or outgoing.
Most computers on the stub domain communicate with each other using the inside local addresses.
Some computers on the stub domain communicate a lot outside the network. These computers have inside global addresses, which means that they do not require translation.
When a computer on the stub domain that has an inside local address wants to communicate outside the network, the packet goes to one of the NAT routers.
The NAT router checks the routing table to see if it has an entry for the destination address. If it does, the NAT router then translates the packet and creates an entry for it in the address translation table. If the destination address is not in the routing table, the packet is dropped.
Using an inside global address, the router sends the packet on to it's destination.
A computer on the public network sends a packet to the private network. The source address on the packet is an outside global address. The destination address is an inside global address.
The NAT router looks at the address translation table and determines that the destination address is in there, mapped to a computer on the stub domain.
The NAT router translates the inside global address of the packet to the inside local address, and sends it to the destination computer.
NAT overloading utilizes a feature of the TCP/IP protocol stack, multiplexing, that allows a computer to maintain several concurrent connections with a remote computer (or computers) using different TCP or UDP ports. An IP packet has a header that contains the following information:
Source Address - The IP address of the originating computer, such as 201.3.83.132
Source Port - The TCP or UDP port number assigned by the originating computer for this packet, such as Port 1080
Destination Address - The IP address of the receiving computer, such as 145.51.18.223
Destination Port - The TCP or UDP port number that the originating computer is asking the receiving computer to open, such as Port 3021
The addresses specify the two machines at each end, while the port numbers ensure that the connection between the two computers has a unique identifier. The combination of these four numbers defines a single TCP/IP connection. Each port number uses 16 bits, which means that there are a possible 65,536 (216) values. Realistically, since different manufacturers map the ports in slightly different ways, you can expect to have about 4,000 ports available.

2006-03-16T15:31:00.000+08:00

Network Address Translation (NAT)

The Internet has grown larger than anyone ever imagined it could be. Although the exact size is unknown, the current estimate is that there are about 100 million hosts and more than 350 million users actively on the Internet. That is more than the entire population of the United States! In fact, the rate of growth has been such that the Internet is effectively doubling in size each year.

So what does the size of the Internet have to do with NAT? Everything! For a computer to communicate with other computers and Web servers on the Internet, it must have an IP address. An IP address (IP stands for Internet Protocol) is a unique 32-bit number that identifies the location of your computer on a network. Basically, it works like your street address -- as a way to find out exactly where you are and deliver information to you.

When IP addressing first came out, everyone thought that there were plenty of addresses to cover any need. Theoretically, you could have 4,294,967,296 unique addresses (232). The actual number of available addresses is smaller (somewhere between 3.2 and 3.3 billion) because of the way that the addresses are separated into classes, and because some addresses are set aside for multicasting, testing or other special uses.

With the explosion of the Internet and the increase in home networks and business networks, the number of available IP addresses is simply not enough. The obvious solution is to redesign the address format to allow for more possible addresses. This is being developed (called IPv6), but will take several years to implement because it requires modification of the entire infrastructure of the Internet.

The NAT router translates traffic coming into and leaving the private network.
This is where NAT (RFC 1631) comes to the rescue. Network Address Translation allows a single device, such as a router, to act as an agent between the Internet (or "public network") and a local (or "private") network. This means that only a single, unique IP address is required to represent an entire group of computers.
But the shortage of IP addresses is only one reason to use NAT

2006-03-15T23:13:00.000+08:00

CONFIGURING OSPF

To enable OSPF in Cisco router :
Router(config)#router ospf process-id
Process-id is an internally used number to identify whether you have multiple ospf process running within a single router.
Process-id is of local significance only

Running multiple ospf processes on same router is not recommended.

Identify which ip networks on the router are part of OSPF network
Router(config-router)#network address wildcard-mask area area-id

VERIFYING OSPF OPERATIONS

•Show ip protocol
•Show ip route [ospf]
•Show ip ospf interface
•Show ip ospf
•Show ip ospf neighbor [type number] [neighhbor-id] [detail]
•Show ip ospf database
•Clear ip route *A.B.C.D
•Debug ip ospf adj

2006-03-15T22:46:00.000+08:00

OSPF (OPEN SHORTEST PATH FIRST)

•OSPF is a Link State Routing Protocol define in (RFC 1131/1247/1583). OSPF version 2 is in RFC 2328, 1998.
•Is a interior gateway protocol (IGP)
•It builds a complete topology map of the network.
•Use Dijkstra’s algorithm to complete the shortest path to each network, thus requires more CPU power to determine route.
•Maintains a Topological Database to a destination which allows OSPF routers to find an alternative route much faster than a RIP router (faster convergence).
•Design for large, scalable internetworks

ADVANTAGES OF OSPF

•OSPF is not dependent upon hop count for choosing the optimal path.
•Highlights of OSPF standard
–Speed of convergence
–Support Variable length subnet masks.
–OSPF updates procedures (better bandwidth utilization)
–Multi-path selection
–Least cost routing
–Routing authentication
–Area routing (support scalable network)

OSPF TERMINOLOGY

•Neighbour
–Referes to a connected (adjacent) router that is running an OSPF process with the adjacent interface assigned to the same area.
•Adjacency
–Refers to the logical connection between a router and its corresponding designated routers and backup designated routers
•Link
–Refers to a network or router interface assigned to any given network.
•Interface
–Is the physical interface on the router
•Designated router (DR)
–Is used only when OSPF router is connected to a broadcast (multi-access) network
•Backup Designated router (BDR)
–Is a hot standby for the Designated Router on broadcast (multi-access) network.
•OSPF Area
–Areas used to establish a hierarchical network.

NETWORK TYPE

Three types of OSPF networks :
Broadcast Networks - network with more than two routers to share a
common network.

Non-Broadcast - network with more than two routers connected Networks to the same network but does not offer broadcast /multicast functionality.

E.g. frame relay.

Point-to-Point - network that connects a single pair of routers.
Network E.g. leased line.

2006-03-15T22:37:00.000+08:00

EIGRP Troubleshooting Commands

Show ip route eigrp
Show ip eigrp neighbors
Show ip eigrp topology
Show ip eigrp traffic
Show ip protocol
Show ip eigrp interface
Debug eigrp packet

2006-03-15T22:02:00.000+08:00

CONFIGURING EIGRP

•Basic configuration of EIGRP on a Cisco Router is identical to that of IGRP
Router(config)#router EIRGP ASno
Router(config-router)# network N.N.0.0
–NETWORK statement identifies the interfaces out of which EIGRP will advertise routing information.
–For each interface EIGRP advertises out, EIGRP includes the network/subnet for that interface in its advertisements.

EXAMPLE

R2(config)#router eigrp 64518
R2(config-router)#network 172.16.0.0
R2(config-router)#network 172.17.0.0
R2(config-router)#network 172.18.0.0

EIGRP IP Address Summarization

Router(Config)# router EIGRP 64512
Router(Config-router)# no auto-summary

No auto-summary : disable route summarization. EIGRP still automatically summarizes at class full boundaries.

2006-03-15T21:48:00.000+08:00

LOAD BALANCING

•Load balancing involves spreading traffic through four or more paths, all reaching the destination in a timely manner.
•Load balancing breaks down congestion, add stability
•Routes with metric equal to the minimum metric will be installed in the routing table (equal-cost load balancing)
•Up to six entries in the routing table for the same destination
–Number of entries is configurable
–Default is four

2006-03-15T21:32:00.000+08:00

EIGRP ROUTING METRICS

EIGRP provides a wide range for its metrics.
EIGRP uses a combination (vector) of metrics
- Bandwidth, delay, reliability, load .

EIGRP metric =
{(K1*Bandwidth) + [(K2*Bandwidth)/(256-load)] + (K3*Delay)} + K5/(Reliability+K4)]
Default K value : K1 =1, K2=0, K3=1, K4=0, K5=0

Default weightings (bandwidth, Delay) is used automatically to calculate optimal routes.
Network administrators can influence route selection .
Weighting factors for each metrics can set by network administrator.

•Administrative distance of EIGRP:
90 for internal routes
and 170 for external routes.

•IOS Command to make change to administrative distance.
distance 1 ~ 255

2006-03-15T21:21:00.000+08:00

EIGRP TABLES

•EIGRP keeps three tables in memory at any given time
–Neighbour table
–Topology table
–Routing table

•Neighbour table
–Is a listing of directly connected neighbours
–Used to house information concerning other EIGRP neighbours
–After learning, records each neighbours’ address and interface.

•Show ip eigrp neighbors

LabrouterA#sh ip eigrp neighbors
IP-EIGRP neighbors for process 88
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
3 172.30.0.3 Fa0 10 00:12:21 4 200 0 40
2 192.168.10.11 Se0 12 00:24:33 114 684 0 13
1 192.168.12.11 Se2 10 00:24:40 88 528 0 15
0 192.168.11.11 Se1 13 00:24:49 13 200 0 17

•Topology table
–Where all route information resides.
–Contains all destinations that neighbours routers advertise and the interfaces through which to dispatch packets destined for those networks.
•Show ip eigrp topology

P 192.168.10.0/30, 1 successors, FD is 20512000
via Connected, Serial0/1
P 192.168.11.0/24, 1 successors, FD is 20537600
via 172.16.10.12 (20537600/20512000), Ethernet0/0
P 172.16.0.0/16, 1 successors, FD is 281600
via Connected, Ethernet0/0

•Routing table
–Contains the listing of the calculated “best” routes to known destination network.
–Also known as route database where the best routes are stored.

•Show ip route eigrp

D 172.17.0.0/16 [90/2195456] via 192.168.11.11, 00:31:09, Serial1
D 172.16.0.0/16 [90/2195456] via 192.168.10.11, 00:30:54, Serial0
D 172.19.0.0/16 [90/2198016] via 172.30.0.3, 00:18:41, FastEthernet0
D 172.18.0.0/16 [90/2195456] via 192.168.12.11, 00:31:01, Serial2
D 172.21.0.0/16 [90/2198016] via 172.30.0.3, 00:18:41, FastEthernet0
D 172.20.0.0/16 [90/2174976] via 172.30.0.3, 00:18:41, FastEthernet0
D 192.168.21.0/24 [90/2172416] via 172.30.0.3, 00:18:41, FastEthernet0
D 192.168.20.0/24 [90/2172416] via 172.30.0.3, 00:18:41, FastEthernet0
D 192.168.22.0/24 [90/2172416] via 172.30.0.3, 00:18:41, FastEthernet0

Show ip route

Gateway of last resort is not set
C 192.168.12.0/24 is directly connected, Serial2
192.168.31.0/32 is subnetted, 1 subnets
C 192.168.31.250 is directly connected, Loopback0
C 192.168.10.0/24 is directly connected, Serial0
D 172.17.0.0/16 [90/2195456] via 192.168.11.11, 00:30:02, Serial1
D 172.16.0.0/16 [90/2195456] via 192.168.10.11, 00:29:47, Serial0
D 172.19.0.0/16 [90/2198016] via 172.30.0.3, 00:17:35, FastEthernet0
D 172.18.0.0/16 [90/2195456] via 192.168.12.11, 00:29:54, Serial2
D 172.21.0.0/16 [90/2198016] via 172.30.0.3, 00:17:36, FastEthernet0
D 172.20.0.0/16 [90/2174976] via 172.30.0.3, 00:17:36, FastEthernet0
C 172.30.0.0/16 is directly connected, FastEthernet0
C 192.168.11.0/24 is directly connected, Serial1
D 192.168.21.0/24 [90/2172416] via 172.30.0.3, 00:17:36, FastEthernet0
D 192.168.20.0/24 [90/2172416] via 172.30.0.3, 00:17:39, FastEthernet0
D 192.168.22.0/24 [90/2172416] via 172.30.0.3, 00:17:39, FastEthernet0

2006-03-15T21:01:00.000+08:00

EIGRP(ENCHANCED INTERIOR GATEWAY ROUTING PROTOCOL)

•Cisco introduced an enhanced version of IGRP on IOS Software Release 9.21. EIGRP is an enhanced version of IGRP.
•Is a Cisco proprietary classless routing protocol
•Considered as a hybrid routing protocol as it combines the advantages of link state protocols with the advantages of distance vector protocols.
•Based on distance vector but has improved convergence properties and the operating efficiency.
•EIGRP is network layer protocol independent and support AppleTalk, IP and Novell IPX.

WHAT IS EIGRP

•Advance distance vector routing protocol
•Also know as hybrid routing protocol
•A combination of best of distance vector and link state routing protocol
–Combines very fast convergence with lower memory requirement and less processor utilization and get its speed and efficiency by acting as link-state protocol
–Operation is primarily distance vector protocol
•When an update is received by a router, it will flood the update to all routers in the entire network
•When a routing change is necessary, updates are send directly to connected neighbours, who in turn update their neighbours.

HYBRID ROUTING PROTOCOL

•EIGRP is based on Distance Vector routing protocol but has the characteristics of Link State routing protocol
–Sends updates only to directly connected neighbours like DV protocol but in a reliable fashion
–Sends route information rather than link-state information in its updates but information need not be sent to all routers in an AS.
–Use DUAL to shares detailed information regarding the best loop-free path to a given destination.
–DUAL reduces the routing protocol overhead traffic.
–Use split-horizon to prevents routing loops.
–EIGRP use a proprietary mechanism to guarantee ordered delivery of some of its messages. EIGRP update and query/reply packets use Cisco Reliable Transport Protocol (RTP).

EIGRP FEATURE AND OPERATIONS

•Relatively simple to configure
•DUAL is use to provide virtually free of routing loops and has a fast convergence time.
•Consumes less bandwidth and router internal resources
•Support VLSM (variable length subnet mask) and automatic route aggregation
•Allows for routing of discontiguous subnets without confusing or overlapping route aggregation
•Employs a reliable transport protocol (RTP) to ensure that routing updates are successfully exchanged between neighbours.
•Support multiple network protocols, maintaining separate neighbour, topology, and routing tables for each protocol, and allow for automatic route redistribution between IGRP, IPX SAP and RTMP.

2006-03-15T17:50:00.000+08:00

OSPF (OPEN SHORTEST PATH FIRST) AND EIGRP(ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL)

OSPF: Open Shortest Path First

Link-state routing

Very infrequent broadcast updates

Extremely granular metrics

EIGRP: Enhanced IGRP

Hybrid routing protocol

Uses distance vectors, however they are triggered by changes, not timers.

Faster convergence, multiprotocol support

Link-state

No-second hand info, and understands entire network

Uses LSP packets to build ‘personal’ copy of entire network structure to route from

LSP: link-state packets or “hello packets”

Chooses ‘best’ path based on: bandwidth, congestion, metrics, etc.

Update times can be set very lengthy as changes cause triggered udpates.

2006-03-10T19:46:00.000+08:00

Revision Question on Subnet Mask

1.If a host on a network has the address 172.16.45.14/30, what is the address of the subnetwork in which this host belongs to?

A. 172.16.45.0
B . 172.16.45.4
C. 172.16.45.8
D. 172.16.45.12
E. 172.16.45.18

Answer: D

2006-03-09T10:04:00.000+08:00

Dynamic Routing

Add the RIP(routing information protocol) routing protocol to your configuration.

RIP is a distance vector routing protocol that uses hop count as its metric. The maximum hop count is 15 so 16 hops is deemed unreachable.

RIP updates are broadcast every 30 seconds by default.

RIP is enabled by typing.

Router(config)#router rip

This puts you in router configuration mode. You then have to associate attached networks with the RIP process. You only associate directly attached networks.

Router(config-router)#network 192.168.10.0

This would add the 192.168.10.0 network to the routing process.

Add the IGRP routing protocol to you configuration.

IGRP is a distance vector routing protocol designed by Cisco(You can only use cisco routers in this siutation since this protocol is CISCO propertiary). The maximum hop count is 255 default is 100 and it uses a combination of variables to determine a composite metric.

Bandwidth

Delay

Load

Reliability

Maximum Transmission Unit (MTU)

Only Bandwidth & Delay is used by default

Routing updates are sent at 90 second intervals by default.

IGRP is enabled by typing

Router(config)#router igrp 12

Where 12 is the autonomous system number.

You then have to associate directly connected networks in the same way as you did with RIP

Router(config-router)#network 192.168.20.0

This would add the 192.168.20.0 network to the routing process.

List problems that each routing type encounters when dealing with topology changes and describe techniques to reduce the number of these problems.

Distance Vector Concept

Distance vector based routing algorithms pass periodic copies of a routing table from router to router. Regular updates between routers communicate topology changes.

Each router receives a routing table from its direct neighbour and increments all learned routes by one.

This is the way that the algorithm learns the internetwork topology, via second hand information. Distance Vector algorithms do not allow a router to know the exact topology of an internetwork.

RIP and IGRP are Distance Vector Routing Protocols.

Distance Vector Topology Changes

When the topology in a distance vector network changes, routing table updates must occur. As with the network discovery process topology change notification must occur router to router.

Distance Vector protocols call for each router to send its entire routing table to each of its adjacent neighbours.

When a router receives an update from a neighbouring router, it compares the update to its own routing table. If it learns about a better route (smaller hop count) to a network from its neighbour, the router updates its own routing table.

Problems with Distance Vector

Distance Vector routing protocols are prone to Routing Loops and counting to infinity.

Routing loops can occur if the internetwork’s slow convergence on a new configuration causes inconsistent routing entries.

Counting to infinity continuously loops packets around the network, despite the fundamental fact that the destination network is down.

To over come these you can implement

Defining a maximum number of hops.

Specify a maximum distance vector metric as infinity. 16 with RIP and 256 with IGRP.

Split Horizon

If you learn a protocol’s route on an interface, do not send information about that route back out that interface.

Route Poisoning

Information past out on an interface it was learned from is marked as unreachable by setting the hop count to 16 for RIP

Hold Down Timers

Routers ignore network update information for some period.

2006-03-02T13:17:00.000+08:00

Routing

Static Routing
Manually added routes

Dynamic Routing
Self-learned routes. E.g. RIP (Routing Information Protocol), OSPF , EIGRP ETC.

Administrative Distances
Trustworthiness of a routing information

The lower the value, the higher the trustworthiness
The higher the value, the lower the trustworthiness

What is an administrative distance of 0?

0 is the default administrative distance for directly connected routes. The router trusts a 0 distance the MOST.

What is the administrative distance used for in static routes?

To rate the source’s trustworthiness. Same as dynamic, it assigns the weighted averages of the links, 255 is the last resort, least trusted.

Static routes are used for which of the following?

Defining a path to an IP destination network. Building routing tables to remote networks.

What is the command that you should use when using static and default routes with your Cisco routers?

The ip classless command tells the router to expect subnetted internetworks on its interfaces. Default is classful mode, which means they look for an entire address class on each interface and do not consider the subnets when making routing decisions.

What is the command syntax to set a gateway of last resort in your Cisco router?

“ip route 0.0.0.0 0.0.0.0 Next hop address” sets a gateway of last resort, or default.

Which Cisco IOS command can you use to see the routing table?

“sh ip route” shows the IP protocol routing table maintained in the router. Sh ipx route will show IPX.

What are three ways that routers learn paths to destinations?

Static, default or dynamic routing.

When should you use static routing instead of dynamic routing?

When you have very few routers and want to save bandwidth. Dynamic routing takes up a great deal of bandwidth. On a slow WAN link static routes may be a better solution.

What are three ways to build routing tables?

Router learns routes by default, statically, or dynamically.

What is the command syntax for creating an IP static route in a Cisco Router?

IP route destination_network subnet_mask default_gateway

How do you create a default route?

By using all zeros to specify the remote network and the subnet mask. The router will use this route as the gateway of last resort.

When looking at a routing table, what does the “S” mean?

Statically connected

What is true about IP routing?

A device will send a frame with the hardware destination or the default gateway. The router will strip the frame and put the datagram in a new frame with the new remote destination address.

What static route parameter will tell a router the name of the interface to use to get to a destination network?

INTERFACE , “ip route INTERFACE ”

The interface parameter is rarely used, but can be used to tell a router what interface to use for a route to a remote network.

When creating a static route, what is the gateway parameter used for?

Defining the next hop.

What does a router do with a received packet that is destined for an unknown network?

It will drop the packet and send an ICMP reply to the sending host.

What is true when creating static routes?

Gateway is required, the administrative distance is optional.

“ip route INTERFACE ”

Interface not required.

When looking at a routing table, what does the “C” mean?

Directly Connected

2006-03-02T12:35:00.000+08:00

Different Modes in Command Line

> : User Mode , very restricted can only troubleshoot but cannot change configurations in this mode
#: Priviledge Mode, can do more than troubleshooting than just reading configurations
To go from User Mode to Priviledge type >enable and drop to #

Enchanced Editing Features

Enhanced Editing features: CTRL-A returns to the beginning of a line, CTRL-B is a backspace, CTRL H, is a destructive backspace, CTRL-P cycles through the command history, CTRL-L reloads the previous line, CTRL-K clears the line, ESC-B moves back one word at a time. Enhanced Editing is enabled by default.

ROM used by the router to store the bootstrap startup, the OS and the POST.

FLASH is an erasable ROM that holds the OS image and the microcode. Retained even if the router is turned off and is the default load.

RAM provides caching and packet buffering. Cleared when the router is turned off.

NVRAM stores the routers startup configuration file. Retains info if router is turned off.

Interfaces are located on either the motherboard or as separate modules for upgrades. If no NVRAM, the router enters the “question driven config dialog.” know as the setup mode

Executive Command Interpreter

1. User mode > is for ordinary tasks like checking status and viewing system info.

2. Privileged Mode #has both user mode commands and allows access to test, debug, and access global configurations. Enter using “en” or “enable”

CTRL+A beginning of command line.

CTRL+E end of command line.

Tab completes the entry for you.

2 Basic Configurations for each router:

1. Startup – held in NVRAM and accessed when the router is started and places config into DRAM. Type “sh startup-config” or “sh star”

2. Running – type in “config t” and you can make changes to the running configuration. When you have it set the way you want, type “copy running-config startup-config” and this new edit of the config will be the new startup config.

Erase startup-config will kill everything in NVRAM and return to the initial configuration dialog.

Virtual Terminal Password “line vty 0 4, login, password , ^Z”

Aux Port Password “line aux 0, login, password , ^Z”

Console Password “line con 0, login, password , ^Z”

Banner “banner motd #, #, end”

“Hostname router A, ^Z”

Change the administrative state of the router's interfaces use shutdown, and no shut.

“write erase” or “erase startup-config” then can run reload.

By default Cisco router are DTE devices, yet without a CSU/DSU to control the clocking, we can set another router to run as a DCE device and set clock rate.

What is the syntax to add a banner to a Cisco router configuration?

Banner motd #. Type in message and end with #.

What command do you use to change your enable password?

In config mode, “enable password ”

How do you change your enable secret password?

In config mode, “enable secret ”

Which of the following will change your Telnet password?

In config mode, line vty 0 4 , login , password ”

What command can you use to copy the configuration from NVRAM into running RAM?

“copy star run” to put the config into RAM. Move new config to startup with “copy running-config startup-config”.

What is the syntax for changing the name of a Cisco router?

Hostname

To exit from privileged mode back to user mode, what do you type at the privileged mode prompt (#)?

Type disable to exit privileged mode.

What is the AUX port used for?

Modem connections for a console or a dialup connection for temporary Dial on Demand Routing (DDR).

When attaching a console cable to your router, how do you log in to user mode?

Press return, type password if prompted.

If the advanced editing feature has been disabled, how do you then enable the advance editing features?

Type “terminal editing”. However advanced editing is enabled by default. Turn off using “terminal no editing”.

CTRL+A will provide what function?

Takes the cursor to the beginning of the line for editing.

What key do you use to view the last command that was entered into a Cisco router?

CTRL-P or the up arrow will allow you to scan recent commands entered.

What key do you press to have the Cisco IOS finish typing a command for you?

TAB will complete a command word.

What does the erase startup-config command do?

Erases the startup-config. Same as wr erase. This will erase the config in the router’s NVRAM and land back into the initial config dialog.

2006-03-02T09:21:00.000+08:00

SETUP MODE

2 Options :

Basic Management
Extended Setup

Basic allows you only basic configuration to allow connectivity to router
Extended allows configuration of global parameters and interface configuration parameters

Setup Mode allows configuration of 2 kinds of enable passwords:
Enable
Secret

Secret is encrypted while Enable is in clear. If Secret is configured enable will not be in used

Telnet passwords are also configured in setup mode. Note if Telnet passwords are not configured then we will not be able to Telnet

You can proceed to configure ISDN parameters, Async parameters, interfaces' IP addresses, hostnames etc. before exiting or you can exit setup mode anytime by using CTRL-C

You can go back to setup mode by typing setup command at IOS CLI ( COMMAND LINE INTERFACE) which I will be covering next

2006-03-02T09:18:00.000+08:00

BRINGING UP A ROUTER

CCNA

Just like PC , the CISCO router whether it be 2500 or 2600 will undergo POST(POWER-ON-SELF-TEST)
After POST, the router will look for IOS in flash memory(EEPROM) of CISCO router
Thereafter, router will look for a file known as "startup-config" in the NVRAM to load the router's configuration
If there isn't a "startup-config" file, the router will automatically goes into SETUP mode

2006-03-02T09:15:00.000+08:00

PERFORMING AN INITIAL CONFIGURATION ON A ROUTER

CISCO ROUTER IOS(INTERNETWORKING OPERATING SYSTEM)
CCNA

IOS powers both CISCO routers and some CISCO switches like Catalyst 2950
Connection to a CISCO device is via modem into the AUX port or event Telnet OR even SSH (SECURED SHELL) if the IOS supports SSH feature.
Access to the IOS Command line is known as the EXEC session
Note that for first setup of a "fresh" device, it will come with a console cable for us to connect via console port to configure the router
Telnet is only performed when network is up and running

2006-03-02T09:12:00.000+08:00

CONFIGURING IP ADDRESSES, SUBNET MASKS, AND GATEWAY ADDRESSES ON ROUTERS AND HOSTS

Configuring Subnet Masks

Subnetting

We need to do subnet so that we can save on IP addresses
Subnetting also allows further segregation of broadcast traffic
Subnetting allows simplified management of network

How to create Subnets ?

Draw out the network diagram
Determine the number of networks (One for each subnet & one for each WAN connection)
Determine the number of hosts in each subnet(One for each host, One for each router interface)
Note we normally use .1 for the router interface to signify gateway address
Upon determining of the above, come out with a subnet mask for the entire network
Determine the subnet-ID for each physical segment
Determine the range of hosts'-IDs for each subnet

CIDR(CLASSLESS-INTER DOMAIN ROUTING)
Short notation for representation of subnet mask

Lists of subnet masks & its CIDR notation
255.0.0.0 /8
255.128.0.0 /9
255.192.0.0 /10
.
.
.
.
255.255.0.0 /16
.
.
.
.
255.255.255.0 /24
.
.
.
.
255.255.255.252 /30

Note: must keep at least 2 bits for hosts at least

PRACTICE EXAMPLE
Subnet 192.168.10.0 using Mask 255.255.255.192

How many subnets?
2^2 -2 = 2

How many hosts per subnet?
2^6-2 = 62

Valid subnets?
256 - 192 = 64
block size = 64
valid subnets are 64 & 128

Broadcast address in each subnet? Valid hosts in each subnet?
For subnet 64
first host = 65
Last host = 126
Broadcast = 127 (one number before next subnet)

For subnet 128
first host = 129
Last host =190
Broadcast = 191 ( one number before 192)

VLSM

Variable Length subnet masks
Know how to use various block sizes to design the network to save on ip addresses

2006-03-02T09:08:00.000+08:00

DESIGNING AN IP ADDRESSING SCHEME TO MEET DESIGN REQUIREMENTS

IP Address :
numeric id assigned to MACHINE on IP network. It always has a network id ( similar to country code, area code in phone numbers) & host id (phone numbers) to uniquely identify itself on the network

IP Terminology:

Bit : 1,0
Byte: 8 bits
Octet: same as Byte, 8 bits

Network Address:
Network address is the designation used in routing to send packets to a remote network - for example 10.0.0.0, 172.16.0.0 and 192.168.10.0

Private IP Address:

Not routable on the public internet
Only used on LAN to hide itself from the public internet
Examples are : 10.0.0.0 , 19.168.0.0 , 172.16.0.0 & 172.31.0.0

NAT(Network Address Translation):

Used to translate private to public address so that hosts can go public internet
3 types of NAT : DYNAMIC NAT, STATIC NAT & NAT OVERLOAD OR PAT(PORT ADDRESS TRANSLATION)

CLASSES OF IP ADDRESSES:
CLASS A : X.Y.Z.W where X represents the network-id and Y, Z, W the host-id
X ranges from 1 to 126 with default mask of 255.0.0.0

The bit pattern for X is by default first bit turn off for X i.e. 0 for the first bit of X according to RFC

CLASS B : X.Y.Z.W where X & Y represents the network-id and Z, W the host-id
X ranges from 128 to 191 with default mask of 255.255.0.0

The bit pattern for X is by default turn on for first bit & turn off for second bit i.e. 1 0 for the first 2 bits of X according to RFC

CLASS C: X.Y.Z.W where X,Y& Z represents the network-id and W the host-id
X ranges from 192 to 223 with default mask of 255.255.255.0

The bit pattern for X is by default turn on for first 2 bits and turn off for the third bit i.e. 1 1 0 for the first 3 bits of X according to RFC

CLASS D & E reserved not used. CLASS D for multi-casting & CLASS E for scientific research

2006-03-02T09:04:00.000+08:00

DESIGNING A SIMPLE LAN USING CISCO TECHNOLOGY

CCNA

TIPS :

Understand the differences between hub, bridge, switch & router.
Understand the terms collision domain versus broadcast domain.
Understand the 7 layers of OSI model including examples to each of the layers. (All People Seems To Need Data Processing)
A- layer 7 Application
P- layer 6 Presentation
S- layer 5 Session
T- layer 4 Transport
N -layer 3 Network
D - layer 2 Datalink
P - layer 1 Physical

Routers:
layer 3 device
route packets
logical separation of LOCAL AREA NETWORKs - subnetting, create different broadcast domains.

Switches:
layer 2 device
switch frames
create one broadcast domain but separate different collision domains
Each and every port in switches create its own collision domains

Note : Switches create separate collision domains, but only one broadcast domain. Routers create separate broadcast domains.

Bridges:
Same functionality as switch except lower in specification like number of ports
Normally fewer ports than switch

Hubs:
lowest end of the above equiptment
Does not separate collision domains & broadcast domains at all

Note: router breaks up broadcast domains for every LAN interface, but it also breaks up collision domains as well

2006-03-02T08:59:00.000+08:00

CCNA EXAM OBJECTIVES

Objectives
The following topics listed are the most likely ones on which the testing will focus during the exam. Topics related to this may probably be tested further in detail too.

Planning & Designing
- Design a simple LAN using Cisco Technology
- Design an IP addressing scheme to meet design requirements
- Select an appropriate routing protocol based on user requirements
- Design a simple internetwork using Cisco technology
- Develop an access list to meet user specifications
- Choose WAN services to meet customer requirements
- Implementation & Operation
- Configure routing protocols, given user requirements
- Configure IP addresses, subnet masks, and gateway addresses on routers and hosts
- Configure a router for additional administrative functionality
- Configure a switch with VLANS and inter-switch communication
- Implement a LAN
- Customize a switch configuration to meet specified network requirements
- Manage system image and device configuration files
- Perform an initial configuration on a router
- Perform an initial configuration on a switch
- Implement access lists
- Implement simple WAN protocols

Troubleshooting
- Utilize the OSI model as a guide for systematic network troubleshooting
- Perform LAN and VLAN troubleshooting
- Troubleshoot routing protocols
- Troubleshoot IP addressing and host configuration
- Troubleshoot a device as part of a working network
- Troubleshoot an access list
- Perform simple WAN troubleshooting

Technology
- Describe network communications using layered models
- Describe the Spanning Tree process
- Compare and contrast key characteristics of LAN environments
- Evaluate the characteristics of routing protocols
- Evaluate TCP/IP communication process and its associated protocols
- Describe the components of network devices
- Evaluate rules for packet control
- Evaluate key characteristics of WANs

On top of that, "DO NOT TAKE THE EXAM" if you are not familar with the maths of IP subnetting calculations , Supernetting etc.

You should also be familar with router commands to configure all the routing protocols including OSPF , EIGRP.

Lastly , be familar with access-lists & extended access-lists on blocking / permitting relevant IP traffic.

2006-03-02T08:56:00.000+08:00

TIPS FOR TAKING THE CCNA EXAM

Tips for taking the CCNA exam

No. of questions = 50 to 65 (depending on your ability)
Duration = 90 minutes
Passing score = 85 percent or more

Test Format:

Multiple choice single answer
Multiple choice multiple answer
Drag & Drop
Fill-in-blank
Router simulations

General Tips:

Read questions carefully don't jump to conclusions too fast as answers maybe very close so do not be tricked by the answers , "read between the lines".

Use the process of elimination to filter out obvious nonsenscial answers. After the elimination process, the odds of getting the right answers will be higher.

There is no review back after you have answered your questions so make sure you have made the right choice before proceeding to the next question.

Good Luck !!!! If you have any questions & comments that you need to contact me. Drop me a mail at jyeesg@gmail.com

2006-03-02T08:38:00.000+08:00

WHY CCNA?

In today's competitive IT marketplace, getting a job in the IT industry or in particularly in the infrastructure & networking arena requires someone to show proof to his /her prospective employer that they are able to do the job well.

Of course, you can mention that you have a wealth of experience troubleshooting / implementing complex network & servers but ultimately a good pass in the CCNA exam still will be a good testimonial or competitive edge to you getting the job , compared to someone who has the same working experience but no relevant certification.

CCNA short for CISCO CERTIFIED NETWORK ASSOCIATE certification is a renowned networking certification in the IT industry that an experienced IT professional should add on to his portfolio for future career enhancements.