iBGP causing routing loop.

[vaultnetworks]

Network Setup:

IBR1 --- CAR1 ---Point to Point-- CAR3 ---IBR3

IBR1  -- Sup720-3BXL Running latest SXJ code. (OSPF + BGP)
CAR1 – Sup engine II. Running old code (OSPF)
CAR3 – Sup engine II. Running old code (OSPF)
IBR3  -- Sup720-3BXL Running latest SXJ code. (OSPF + BGP)

So I brought a BGP peer up with loopbacks on IBR1 and IBR3 router. They both obtain full routes from the other and appear to work as they should. The problem arises when I run a traceroute on the router that shows in the bgp table to route out to the other side. From IBR1 the packet will show next hop Car1. When the packet arrives at CAR1, due to that ip block not having a routing entry anywhere in the router, it defaults to OSPF’s 0.0.0.0 which heads back to IBR1. Yet the next-hop in bgp session is my /30 on IBR3.

It’s our intent to utilize resources on the other side of the Point to Point for those resources and backup should an IBR fail on either side, but not to force manual routing over it.

My question is: Is there a way to accomplish this without running BGP on CARs with some basic configuration changes or are we looking at having to deploy MPLS to skip over routers that lack enough knowledge?

[Joseph W. Doherty]

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Posting

Are you using next-hop-self?

PS:

After re-reading you posting, doubt usage of next-hop-self if relevant to what you've described.

What it sounds like, the BGP router knows to where correctly go next but when your next physical (IGP) router doesn't have a route for the packet, it defaults to using the default route which sends the packet back to the first BGP router.

Besides MPLS, you could also solve the problem with a GRE tunnel between the two BGP routers, or you might configure a VLAN between the those two routers.

[milan.kulik]

Hi,

another soultion might be using Policy Based Routing.

If you use

set ip default next-hop pointing to CAR3

command in the PBR route-map applied on the CAR1 interface pointing to IBR1  the packets with no routing table entry coming from IBR1 would be routed to CAR3.

(Of course you'd have to make a symmetric configuration on the CAR3 router.)

See

http://www.cisco.com/en/US/customer/tech/tk364/technologies_configuration_example09186a00801f3b54.shtml

or

http://www.cisco.com/image/gif/paws/47121/pbr_cmds_ce.pdf

for examples.

HTH,

Milan

[Kishore Chennupati]

back on those days, they used to redistribute BGP into IGP etc but these days is not recommended.

In your case, you have to run MPLS to get what you want.

HTH,

Regards