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

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
.
.
.
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255.255.0.0 /16
.
.
.
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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