auto summarisation question

arthur1350

i connected two subnets 10.1.0.0/16 and 10.2.0.0/16 to router R1's fast ethernet ports . Then the serial port of R1 was connected to other router R2's serial port. the serial link between routers was in the network 11.0.0.0/8. I enabled rip version 2 on both the routers. So, naturally auto summarisation took place at R1's serial interface and route advertised to R2 was 10.0.0.0/8. What i want to ask is, why not the route 10.0.0.0/14 was advertised as summarisation of 10.1.0.0/16 and 10.2.0.0/16 yields 10.0.0.0/14.....

Rakurai

RIPv2 summarizes the route as a classfull network, which is where it got the 10.0.0.0/8.

arthur1350

Then when does the route gets summarised according to the common bits appearing in the group of contiguous subnets.....Because i have read that this is a way of summarising contiguous subnets.

Rakurai

It would be advertised like that when doing manual summarization of the route. Example for your subnets would be :

ip summary-address rip 10.1.0.0 255.255.0.0

ip summary-address rip 10.2.0.0 255.255.0.0

This command is done on the outgoing interface of the router where you want it to be summarized.

Link to Cisco Doc:

IP Routing: RIP Configuration Guide, Cisco IOS Release 12.4T - Configuring Routing Information Protocol  [Cisco IOS Software Releases 12.4 T] - Cisco Systems