OSPF and BGP routing related

[Jacob Samuel]

Hi,

i hav a customer, they have offices in 2 different cities. as of now the 2 offices are connected over Telco MPLS VPN network. 2 core connecting to failover swithc connecting to singel router at both side. for backup and sysnch they use a dedicated link between two sites. OSPF Runnig from Core, and in the router ospf get redistributed to Telco BGP and vise versa. attaching the diagram for reference.

now customer want another link at one site, and added new circute and router for the same. i want to enable dynamic routing using the same ospf instance on the newly connected router, and want to use the one as a backup/loadbalancing router / link.

what shoudl i do in this? if i configure the similar configuration like what is configured on the Existing router (Router A) would it work? will it make any looping or issue?

appreciate yur immediate response.

regards

Sunny

[paulstone80]

If Router B is to be the backup link, add the router to the same OSPF area, and when you redistribute BGP from the Telco set the metric to be higher than 20.

This will mean BGP routes from Router A will have a metric of 20 (default) and routes from Router B will be higher, and therefore less favoured.

HTH

Paul

[Jacob Samuel]

Thanks Paul.

If i want to use the second link as load balacning link then what should i do in this case.

regards

jacob

[Abzal]

Hi,

I'll try to help you. I assume that two core and routerA/routerB on the same subnet.

If you have default static route like this:

ip route 0.0.0.0 0.0.0.0 x.x.x.x

and same route to second routerB

then redistribute into ospf

routerA/B:

router ospf

redistribute static

maximum path 2

but OSPF does only equal load balancing. So cost from routerA/B to Core1/2 must be the same.

Hope it will help.

[paulstone80]

Hi Jacob,

If you want load-balancing across the two links then distribute BGP into OSPF with the same metric as Router-A. You also need to ensure that the cost to Router-A and Router-B are the same as seen from the Core. It may be worth setting the OSPF interface cost statically on both Router-A, and Router-B, to ensure they match.

As long as both the administrative distance and OSPF cost are the same for each path, the Core router will add both routes into its routing table. The core router will load balance either by Per Destination, or Per Packet as required.

See this link for more info: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094820.shtml

HTH

Paul