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
network 20.0.0.0
default-metric 100000 100 255 1 1500
no auto-summary
!
router ospf 1
log-adjacency-changes
redistribute eigrp 1 subnets route-map EIGRP-to-OSPF
network 10.0.0.0 0.255.255.255 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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