Static route in a multi-homed network and redundant link

Unanswered Question
Oct 19th, 2007

I have a new setup, here we have 3 routers and two ISP.

I am running OSPF and IBGP in my company. Let named then as A, B and C.

A is connected to ISP X and C is connected to ISP Z.

OSPF is running on A, B and C.

IBGP is running on A and C with loop Loopback interfaces address as neighbors address.

I have configured static routes and give default-information originate command under the OSPF process on router A and B.

Router B is loading balancing in a round robin manner.

What I want that one ISP goes down whole traffic to shift to other and when the ISP come back loading start again.

I have this problem too.
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hadbou Thu, 10/25/2007 - 10:05

Benefits of Multipath Load Sharing for Both eBGP and iBGP

The BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS VPN feature allows multihomed autonomous systems and PE routers to be configured to distribute traffic across both eBGP and iBGP paths.

How to Configure BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN :

configure {terminal | memory | network}

router bgp as-number

address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name] | ipv6 [multicast | unicast] | vpnv4 [unicast]

maximum-paths eibgp number [import number

royalblues Thu, 10/25/2007 - 10:38

If i understand your setup you have two routers A & C connected to ISP and are receiving default route from them.

The default is redistributed to OSPF and advertised to B and B is loadbalancing it.

If this is the case, then a cirucit failure would cause all the traffic to flow on the redundant circuit.

If you want to make one circuit as primary, then you can advertise one as an OSPF external type 1 route and the other as a type 2 route. This will make sure that ll traffic uses the router advertising the type 1 route and will fallback to other in case of failure


evsrajatgupta Thu, 10/25/2007 - 11:59

Thank Hadbou,

I have found this out two days back. Now i am in a different issue I have notice that if there is a link failure inside any of the ISP network, I get packet drop.

E.g. If there is a something goes wrong in the ISP network (say ISP X) and a remote IP is not reachable via ISP X. Since by router (B) is load balance on both ISP, every second packet which I think send via ISP X gets drop.

A per now in simple shutdown the interface on which ISP X is connected and the whole traffic to Z. Can this be done automatic?


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