IGP Tagging with BGP AS-Path info

[kfarrington]

Is it possible to have a core BGP network with every site running its own IGP. When the IGP at the edge of the BGP core get redistributed into BGP, to TAG the IGP routes with an IGP AS number, and carry that through to another IGP on the edge after the BGP core.

Another alternative would be to take the BGP AS-Path at the edge and when redistributeing BGP routes into the IGP, to somehow, take the BGP AS-Path and redistribute this as a tag into the IGP.

Pleasze can someone let me know if they have managed to simulate BGP AS-Path to an IGP.

Many thx,

Ken

[owillins]

This can be achieved by route tagging. Tags are supported by IGPs such as eigrp,ospf,is-is, ripv2. For eg. is ospf is your igp, then bgp can use the route tag field to convey as path information to other bgp ASs. You would have to mark the tag as the AS number. Use route-maps when redistributing ospf into bgp and use the set as-path tag command within the route-map. Refer to a case study on route tagging in Routing TCP/IP Volume II by Jeff Doyle for details.

[kfarrington]

That is fantastic - and sorry for the delay in replying.

Whilst this works for a BGP-->OSPF-->BGP topology,

we have the following topology

OSPF-spoke-->BGP-->(mpls network)-->BGP-->OSPF-hub

it would be great if in the hub site we could tag the as-path information to the hub ospf network.

so that in the hub IGP we could see in the OSPF database where that route originated from?

maybe its a crazy idea? It's a nice concept.

Please could you or anyone help further?

Kindest regards,

Ken

[kfarrington]

Sorry - to clarify this point

OSPF-spoke-->BGP-->(mpls network)-->BGP-->OSPF-hub

-------------as5--------------------as6---ospftag 5 6

so in ospf, at the hub, I would like to see a tag in the ospf database showing as 5 (spoke) and as 6 (hub) so from a hub router, I could see that this route originated in as 5.

Many thx, and I hope this is clear :))

Ken