From: Atif Awan (atifawan@xxxxxxxxxxx)
Date: Mon Sep 25 2000 - 05:09:54 GMT-3
I was going through the explanation on CCO about the behaviour of ip
unnumbered with RIP/IGRP. The link to the document is:
http://www.cisco.com/warp/customer/701/20.html
Suppose two router are connected back to back and the serial interfaces of
both of them are using ip unnumbered to their respective ethernet
interfaces. On one router you have a major network 172.16.0.0 with subnets
172.16.1.0/24, 172.16.2.0/24 and 172.16.3.0/24. On the other router you have
a different major network 170.1.0.0 with subnets 170.1.1.0/24, 170.1.2.0/24
and 170.1.3.0/24. RIP has been configured on both the routers and like it is
stated in the CCO doc the routers read the incoming routes from each other
as host routes because the other router is not supposed to be sending the
subnets. This is fine but the article also says that unless you specify a
static route to the other major net you will not have connectivity but when
i configured this in a lab setup each of the routers was also advertising a
network route of its attached major network which enabled the other router
to reach its subnets. I am not saying that the host routes were not there
but there was also no connectivity issues as discussed in the article on
CCO.
The same thing happened with IGRP too. Here is a sample output from the
debug ip igrp transactions command on one of the routers:
IGRP: sending update to 255.255.255.255 via Serial0 (172.16.1.1)
subnet 172.16.4.0, metric=501
subnet 172.16.5.0, metric=501
subnet 172.16.1.0, metric=1100
subnet 172.16.3.0, metric=501
network 172.16.0.0, metric=501 <---- ( this is the network being
advertised which enables the other router to reach this router's subnets)
Can someone shed some light on this please.
Regards
Atif Awan
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