bgp default-information orignate

[singh.andy]

is there any other way to originate a default route in bgp besides default-information. I'm receving a default route via an IGP and would like advertise this to bgp speakers without doing default-information orignate or having network 0.0.0.0 under bgp..

[pkhatri]

You can use the 'neighbor {ip-address | peer-group-name} default-originate [route-map map-name]' to advertise a default on a per-neighbor basis. You can use the route-map to advertise the route conditionally depending on the existence of a default from your IGP.

HTH,

Paresh.

[Harold Ritter]

Just as a clarification, the default-information originate has for only purpose to allow the default route to be redistributed in BGP from another routing protocol or static route. Without this command the default will be rejected by BGP. As another poster indicated "nei x.x.x.x default-originate route-map " is the way to go.

Hope this helps,

[singh.andy]

but let's say i have default-information originate configured and am redistributing igp into bgp to advertise this default out to another bgp speakers..but now one of my ebgp peers also sends me a default route..what would happen in that situation..i want to be able to install this new route that i received into my routing table ...and in case it goes away i want to advertise one out..hope this makes sense

[Harold Ritter]

If you redistribute teh default form IGP into BGP, this default would be locally originated and therefore preferred over the one received from eBGP.

If you do receive a default from one eBGP neighbor, you should be able to just advertise that default to your other neighbors. The only drawback is that if you loose that ebgp neighbor, you will stop advertising the default to the other peers.

If you want to keep advertising the default to your peers even though your eBGP peer advertising the default goes away, you need to use the "neighbor x.x.x default-originate" towards the peers, which you want to receive the default.

Hope this helps,

[singh.andy]

what i am trying to do is receive a default via ebgp peer and install that route into the routing table and in case i stop receving this default from ebgp peer i want to advertise a default to it..ebgp peer is up at all times..

[Harold Ritter]

Andy,

I'm not sure I understand your scenario. You receive a default route from a given eBGP peer and if you stop receiving the default route from that peer you want to advertise a default to that same eBGP peer.

Can you help me understand what you are trying to achieve.

Thanks,

[singh.andy]

that's exactly what i'm trying to do..i have two main datacenters (A and B) each have internet connections..all remote offices are connected via MPLS cloud.Currently datacenter A advertises a dafult to all sites including datacenter B so everyone can use that to go out to the inernet..in case datacenter A is down down i want datacenter B to start advertising this default instead..

[Harold Ritter]

One way you could ahieve that is by using the conditional advertisement feature. On datacenter B, you would monitor for the presence of the default route coming from datacenter A and when it disappears you advertise the local default to the MPLS cloud.

Please refer to the conditional advertisement feature documentation for more information:

http://www.cisco.com/warp/customer/459/cond_adv.html

Hope this helps,

[singh.andy]

thanks..i'll have to test that to see if it works for default routes

[Harold Ritter]

This will work for the default route as well.

Hope this helps,

[dwyerr]

Hello.

Why not just advertise the two routes with different metrics preferring site A.

Something like.

Site A

========

neighbor x.x.x.x default-originate route-map COST-DEFAULT

route-map COST-DEFAULT permit 10

set metric 0

=========

Site B

==========

neighbor x.x.x.x default-originate route-map COST-DEFAULT

route-map COST-DEFAULT permit 10

set metric 5

===========

This way all the sites will have both routes but will prefer site A. When site A goes down there is a route already in the table for Site B. (fast convergance.)

-Rob

[mjoaquin23]

The purpose of your route-map is different from how a route-map under neighbor x.x.x.x default-originate command functions. This route-map functions as a conditional statement to the 0/0's advertisement instance.

Hritter's solution, I think is correct with route-maps containing the following match statements:

match ip address (0/0 ACL #)

match next-hop (ebgp-peer address)---protects the router from 0/0 adverised by an IBGP peer.