Redistribution question

Unanswered Question
Oct 11th, 2008

hi guys,

There's something in Cisco's BSCI Exam guide, 4th Ed, on page 350 (Example 2).

Routers B, C and D are supposed to see both RIP and EIGRP routes, right? On page 352, the configuration 's output shows that we redistribute EIGRP into RIP.

I don't understand why we changed the Admin Distance of routes to 140.100.1.0 and 140.100.2.0 while they are not advertized by EIGRP. I see that they are still RIP routes and so they are not learned from EIGRP.

am I missing something?

I have this problem too.
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Giuseppe Larosa Sat, 10/11/2008 - 10:17

Hello Wassim,

the topology shows multiple routers as border routers between EIGRP and RIP:

RB and RC are RIP neighbors of RA that is internal to RIP domain.

But RA links to RB and RC for example are in major network 140.100/16.

Without increasing the distance:

each of RB and RC will advertise subnets of links to RA directly in EIGRP with AD 90:

the passive-interface e0 avoids to create EIGRP adjacencies on e0 but doesn't stop advertising of the associated IP subnet that is within 140.100/16.

This can lead to suboptimal routing where RC sends via FR cloud packets that could be sent out e0 to RA for subnet 140.100.3.0: packets will go to RE then to RB and then to RA.

By increasing to 200 the admin distance for these prefixes inside router EIGRP the EIGRP routes are not installed and the RIP updates are installed in the routing table avoiding suboptimal routing.

This could be a real concern if in net 140.100.3.0 would be some important servers with high traffic volume in that case avoiding to use the expensive and limited WAN bandwidth for this non-optimal routing would be important.

Another solution could be that of using the network commands with wildcard options so that all E0 IP subnets are not a match.

In that case no internal EIGRP route with AD 90 is created for them.

The example could be more interesting using OSPF as core routing protocol instead of EIGRP where AD of redistributed O Ex is still 110 less then 120 of RIP.

Hope to help

Giuseppe

ccnpninja Tue, 10/21/2008 - 11:31

Could we avoid changing the AD if we suppressed the "network 140.100.0.0" statement under "router eigrp 100"? I don't see the benefit from advertising the same networks with both RIP and EIGRP, then redistributing one into another.

Giuseppe Larosa Tue, 10/21/2008 - 12:27

Hello Wassim,

here to avoid these problems you could use more specific network commands

so that to leave out the interfaces in the RIP domain

network 140.100.x.0 0.0.0.255

have to be used

Hope to help

Giuseppe

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