Understanding the network.pdf - Back to Home

IOS allows you to adjust how the RIP process behaves and interprets route
advertisements.
NOTE
RIP version 1 does not send subnet masks in its update messages. So, networks are
announced using the address space's classful root. Routers then apply their locally
configured subnet mask to interpret the address space. RIP version 2 sends both the
network address and mask in its updates. However, RIPv2 summarizes at network
boundaries, announcing only the classful root. RIPv2 uses the subnet masks on the
corresponding interfaces to construct the subnet mask elements of its update
messages. If you use classless addressing with a large classful space, this can
present problems if discontinuous subnets are used. The RIP subprocess command
disables network summarization.
Adjusting Distance and Metrics
To adjust the administrative distance applied to all route advertisements received
by the RIP process, use the router subcommand .
If you need to change a route's metric, a standard access list is used in combination
with the RIP subcommand . The Albany network has three access points to the
192.168.192.64 /26 network: asbr-a2, asbr-a3 and asbr-a4. In order to make all
three routes have the same cost, the advertisement for the 192.168.192.64
network must be adjusted on asbr-a2. First, a standard IP access-list is created:
asbr-a2(config)#access-list 1 permit 192.168.192.64 0.0.0.0
Then, in the RIP subprocess, the metric adjustment is applied. This adjustment
forces the metric for IP address 192.168.192.64 from 1 to 3 only on announcements
sent to asbr-a1 from asbr-a2:
asbr-a2(config-router)#offset-list 1 out 2 ethernet 0