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Multiple EIGRP autonomous systems in a VRF

A while ago Ron sent me an intriguing question: “Is it possible to have two EIGRP AS numbers in the same VRF?” Obviously he’s working on a network with multiple EIGRP processes (not an uncommon pre-MPLS/VPN solution; I did a network design along the same lines almost 20 years ago).

It’s easy to run multiple EIGRP autonomous systems in the global IP routing table; just create more than one EIGRP process. They can even run over the same set of interfaces. EIGRP-in-a-VRF implementation is slightly different; you configure an address family within another EIGRP process and (optionally) specify an AS number that does not have to match the AS number of the EIGRP process.

My first (pretty lame) reply was obvious: why don’t you create two EIGRP processes and specify the same VRF address family in both? Unfortunately this trick doesn’t work; although you could use multiple EIGRP processes, each VRF can be specified only in one of them.

In the end, I had to admit that the only viable solution is creation of two VRFs (with the same route targets and different route distinguishers), one for each EIGRP AS number. Ron’s reply: “Yeah, I know that works, but I was trying to figure out how to do it within EIGRP. “ Obviously you can’t.

Just in case you’d need to do something similar, here’s the relevant part of the PE-router configuration (note that we’re using eigrp 11 everywhere even though the AS numbers in the VRFs are 1 and 2).

ip vrf Cust_AS_1
rd 65000:1
route-target export 65001:1
route-target import 65001:1
!
ip vrf Cust_AS_2
rd 65000:2
route-target export 65001:1
route-target import 65001:1
!
router eigrp 11
!
address-family ipv4 vrf Cust_AS_1
autonomous-system 1
network 0.0.0.0
no auto-summary
redistribute bgp 65000 metric 128 10000 255 1 1500
exit-address-family
!
address-family ipv4 vrf Cust_AS_2
autonomous-system 2
network 0.0.0.0
no auto-summary
redistribute bgp 65000 metric 128 10000 255 1 1500
exit-address-family
!
router bgp 65000
no synchronization
bgp log-neighbor-changes
!
address-family ipv4 vrf Cust_AS_1
no synchronization
redistribute eigrp 11
!
address-family ipv4 vrf Cust_AS_2
no synchronization
redistribute eigrp 11

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1 comments:

  1. That is cool feature... I would have thought that just creating two EIGRP ASes would resolve the issue. I presume the VRF just splits the single instance of EIGRP and allows a default route? (0.0.0.0)

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