BGP 2nd Default GW to ISP

[John Blakley]

I've attached a diagram. I'm wanting to advertise another default gateway to our ISP via BGP. I want to be able to ensure that this default route also gets put in their table so as to load balance between the 2 sites. Am I going to have to get in touch with the ISP for this?

BGP1 currently is the default gateway for all locations. BGP 2 is a backup site (our DR) that I want to use as another path to the internet via the MAN connection. The Red connection from BGP 3 is the 2nd path that I'd like it to take. I've got a lab set up, but even after changing maximum-paths to 2, it doesn't put the second default route in the routing table.

Thanks!

[Stephane Bonnet]

The configuration of your routers would be welcome.

But if  you are in the same AS, for all the 3 routers, your problem is the fact of the bgp split horizon rule.

BGP-1 advertise certainly via "default-information originate" to BGP-2 and BGP-3 but BGP-2 or BGP-3 doesn't advertise this default route which has been passed by an iBGP peer.

An iBGP peer cannot advertise an iBGP learned route, it's a loop prevention mechanism.

You can build subconfed to override this behavior and make it happen as you want.

HTH

Stephane

[John Blakley]

It's a basic setup at this point. Both my CE routers are advertising 0.0.0.0 into the provider. The provider gets it, but only puts one route in the table:

*  0.0.0.0          172.28.1.1               0             0 65127 i

*>                  172.20.100.1             0             0 65100 i

Currently, my lab doesn't have mpls set up. I can do this if I were expecting a different outcome.

Here's the ISP router:

router bgp 1

no synchronization

bgp log-neighbor-changes

network 172.20.100.0 mask 255.255.255.0

network 172.28.1.0 mask 255.255.255.0

network 172.30.3.0 mask 255.255.255.0

neighbor 172.20.100.1 remote-as 65100

neighbor 172.20.100.1 default-originate

neighbor 172.28.1.1 remote-as 65127

neighbor 172.30.3.1 remote-as 65003

maximum-paths 3

no auto-summary

Thanks!

[milan.kulik]

Hi,

AFAIK, even when maximum-paths command used, both prefixes have to come from the same neighboring AS to be used for BGP load balacing.

See http://www.cisco.com/en/US/customer/tech/tk365/technologies_tech_note09186a0080094431.shtml#bgpmpath

BR,

Milan

[Stephane Bonnet]

Always better with a show command to understand.

Milan find the issue, Thotsaphon on the other post share a wonderfull command to circumvent the issue:

bgp bestpath as-path multipath-relax

Stephane