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

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

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)

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

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

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

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

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.

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.

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.

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.

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.

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

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

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

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.

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

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

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.

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

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.

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

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

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

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.

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.

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

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.

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