Why does ABR sh Null 0 on its routing table after summarization.

[mahesh18]

Hi,

I have question regarding ABR  router in Ospf.When it summarize the address of nei Routers  loopback IP address why  does it show  Null0 in the end in its own routing table

ABR router sh ip route

O       10.10.1.1/32 [110/2] via 192.168.4.3, 00:05:36, FastEthernet0/4

O       10.10.0.0/22 is a summary, 00:05:36, Null0 **********************************************************

O       10.10.0.1/32 [110/2] via 192.168.4.3, 00:05:53, FastEthernet0/4

O       10.10.3.1/32 [110/2] via 192.168.4.3, 00:05:53, FastEthernet0/4

O       10.10.2.1/32 [110/2] via 192.168.4.3, 00:05:54, FastEthernet0/4

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

Have a look at this link for explanation:

http://www.mcmcse.com/cisco/guides/ospf_null_interface.shtml

HTH

[mahesh18]

Hi Reza,

Thanks again.

Mahesh

[Peter Paluch · Accepted solution]

Hi Mahesh,

This topic is being discussed very often. I've been discussing the same issue some time ago in this thread:

https://supportforums.cisco.com/message/3159168#3159168

(look for the "What is the logic behind sending an EIGRP summary route with a NULL0 value." question)

Best regards,

Peter

[mahesh18]

Hi Peter,

Thanks for posting that link.

There you explained the concept very deeply by giving an example.

You are very good in explaining the concepts.

thanks again

Mahesh