RIP / EIGRP advertises static routes

[nimalrajphilips]

Hello everyone,

I  would like to get the explanation for the following.

I have two routers connected with each other and running RIP in between them (Only on directly connected interfaces). On one of the routers there is a static route which is pointing to one of the local interfaces as the exit point. The config are as follows.

Router1

interface fa0/0

ip add 10.10.10.1 255.255.255.0

interface fa0/1

ip add 10.10.20.1 255.255.255.0

router rip

ver 2

no auto

network 10.0.0.0

network 172.16.0.0

ip route 172.16.10.0 255.255.255.0 fa0/1  {I am using the interface as next hop; not the next hop ip address}

Router2

interface fa0/0

ip add 10.10.10.2 255.255.255.0

router rip

ver 2

no auto

network 10.0.0.0

Now, when I do the "Show ip route" command on Router2, I can see the 172.16.10.0 in the routing table though there is no physical interfaces which have 172.16.10.0 network in Router1.

I tried the same with EIGRP as well as with BGP, I am getting the same results. But not with OSPF.

Could any one of you please explain,

1.     Why I am getting this route in the routing table with RIP/EIGRP?

2.     Why I couldnt get this with OSPF?

Cheers

Nimalraj

[Marwan ALshawi]

When you install a static route to an interface, and configure a network statement using

router eigrp, which includes the static route, EIGRP redistributes this route as if it were a directly connected interface When you install a static route to an interface, and configure a network statement using router eigrp, which includes the static route, EIGRP redistributes this route as if it were a directly connected interface

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#statictointerface

i i beleive with OSPF as it is link state and use differnt concept of installing routes with LSAs and link/network type it is not apearing without redistribution command 

hope this help

if helpful rate

[Peter Paluch · Accepted solution]

Hello Nimalraj,

In addition to Marwan's reply, what you are seeing is a known behavior, however, it is not a principial issue but rather a decision of the Cisco internal team that developed and implemented the particular code in IOS. Simply, distance vector protocols (IGRP, EIGRP, RIP) are implemented in such a way that they consider static routes defined with egress interface as directly connected and therefore injectable into the protocol simply by the network command. OSPF considers such routes still as static, not as directly connected, and therefore the network command in OSPF does not apply to them.

Once more - do not try to find any extraordinary logic about this. Specifications of routing protocols do not cover these instances, and it is left purely to the software engineer how he deals with it. What you see is how Cisco in particular decided to do it. It may not be the same with other vendors.

Best regards,

Peter

[SunilKhanna]

Thanks Marwan and Peter, I have been following this discussion and your comments have been very useful.

Regards,

Sunil

[nimalrajphilips]

Hello Pete & Marwan, Thanks alot for the reply. Appreciate your clarification.

Cheers

[Peter Paluch]

Sunil, Nimalraj,

Thank you both for your ratings and kind words!

Best regards,

Peter