02-29-2012 11:41 AM - edited 03-04-2019 03:29 PM
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!
02-29-2012 12:05 PM
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
02-29-2012 12:16 PM
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!
03-01-2012 12:15 AM
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
03-01-2012 12:28 AM
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
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