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New Member

OSPF question

I have a situation were when I issue a show ip route for a particular subnet lets say a.b.12.0/24 I get the following results.

The route is known via OSPF as an E1as a.b.8.0/21, but there are two parts of the response I'm not familiar with: tag custom and path==0.

Could anyone shed any light on their meaning.

The box issuing the show cmd is a 3620 with a 12.2 IOS the next upstream device is a non cisco device both of which are particpating in a non zero ospf area.

The reason I care about these fields is that I can ping a.b.8.1/23 and a.b.14.1/23 but not a.b.12.1/23. The a.b.8.1/21 are on the far side of the network.



Cisco Employee

Re: OSPF question

Hello Benjamin,

This tag and path info is actually coming from bgp table-map feature

to map external entry attribute into the routing table. OSPF is only carrying

these attributes along. You can read more about this in RFC 1403 - BGP OSPF interaction.

I am not sure what is the reason you can not ping that address. I suggest you go hop by hop and see where the ping is actually failing.

Hope it helps,


New Member

Re: OSPF question


Thanks for the thoughs on the problem. At the moment I'm at a loss as to how this route is known by BGP since these routers do not see any BGP at all. The routing fault was indeed

Still will do as you suggest and read 1403 but seening as the solution was as follows I cannot see how BGP has become involved.

The problem was solved when the routing was changed from a redistributed static route to a full OSPF inter area route.



Cisco Employee

Re: OSPF question

Hi Benjamin,

I did not say that this route is "learned" via BGP. All I am saying is that this route was originally redistributed from BGP into OSPF. When you see the OSPF routes on your router, it has this BGP information. I think it will be more clear once you read the RFC.