Saturday, June 19, 2010

Preventing Redistributed Routing Loops

Today I ran over a quick lab of something you may experience in the real world, routing loops due to redistribution. As shown in the picture above, both the routers R1 and R2 are redistributing the same networks both ways. Because of Administrative Distance, each router would think the best route to EIGRP were through each others OSPF interfaces and vice versa which would cause a routing loop.

To circumvent this, I have created a route-map and assigned tags to both routing networks to prevent redistributed routes to be learned in both directions:

(Running Configurations on Both R1 and R2)
router eigrp 1
redistribute ospf 1 route-map OSPF-to-EIGRP
default-metric 100000 100 255 1 1500
no auto-summary
router ospf 1
redistribute eigrp 1 subnets route-map EIGRP-to-OSPF
network area 0
default-metric 100
route-map EIGRP-to-OSPF deny 10
match tag 90
route-map EIGRP-to-OSPF permit 20
set tag 110
route-map OSPF-to-EIGRP deny 10
match tag 110
route-map OSPF-to-EIGRP permit 20
set tag 90

I'm going to be learning about GRE tunnels shortly as well, hopefully it isn't to complicated to grasp, VPN's and tunneling always confused me because I have a habit of over complicating things!

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