Should Have Gone With Cisco

PE-CE routing with EIGRP

This is a continuation from Part II of the MPLS worklog

It’s time to test using an IGP between the PE and CE routers. I decided to start with EIGRP. Compared to using eBGP between the PE-CE routers, IGPs are somewhat more involved. The nice thing about using BGP is you don’t really have to mess with redistribution too much (except for connected or static routes). With an IGP such as EIGRP, you will have to redistribute twice on the PE router. It’s a little strange at first, but once you see the configuration, it should make sense.

First, here is the diagram for Part III

Not much has changed. EIGRP is used between Customer A and provider routers. The EIGRP AS is 1 for both sites. By keeping the EIGRP AS number the same, no “external” EIGRP routes will be seen on Customer A routers (Thanks to BGP extended communities for EIGRP!). So if they were different AS numbers, you would see “D EX” in the routing tables.

Here are some configuration excerpts:

CUST-A-1
!
router eigrp 1
network 10.0.7.192 0.0.0.7
network 10.0.7.224 0.0.0.3
no auto-summary
!

PE1
!
router bgp 500
no synchronization
bgp log-neighbor-changes
neighbor 10.0.7.241 remote-as 500
neighbor 10.0.7.241 description M-BGP to PE2
neighbor 10.0.7.241 update-source Loopback0
neighbor 10.0.7.242 remote-as 500
neighbor 10.0.7.242 description M-BGP to PE3
neighbor 10.0.7.242 update-source Loopback0
neighbor 10.0.7.243 remote-as 500
neighbor 10.0.7.243 description M-BGP to PE4
neighbor 10.0.7.243 update-source Loopback0
no auto-summary
!
address-family vpnv4
neighbor 10.0.7.241 activate
neighbor 10.0.7.241 send-community both
neighbor 10.0.7.242 activate
neighbor 10.0.7.242 send-community both
neighbor 10.0.7.243 activate
neighbor 10.0.7.243 send-community both
exit-address-family
!
address-family ipv4 vrf CUSTOMER_A
redistribute connected
redistribute eigrp 1
no synchronization
exit-address-family
!
!
router eigrp 1
auto-summary
!
address-family ipv4 vrf CUSTOMER_A
redistribute bgp 500 metric 1500 400 255 1 1500
network 10.0.7.224 0.0.0.3
no auto-summary
autonomous-system 1
exit-address-family

First take a look at the BGP vrf configuration for CUSTOMER_A. We are redistributing EIGRP and any connected routes (local interfaces configured with CUSTOMER_A vrf). By bringing the EIGRP routes into this BGP vrf, it allows the EIGRP routes to be exchanged via MP-BGP to the other PE routers. If you don’t do this, you won’t see any of the networks learned via EIGRP show up under the “show ip bgp vpnv4 vrf CUSTOMER_A” command. Remember, our EIGRP networks get exchanged via MP-BGP in the form of VPNv4 routes.

Here is what you see on PE1 as a result of redistributing EIGRP into the BGP vrf:

You can see that the BGP table knows about all networks in each Customer A site (as a result of redistribution configured on each PE router). These routes will be exchanged with the other PE routers and show up in their “CUSTOMER_A” vrf BGP table (and in the Customer A vrf routing table as “B”). So for example, 10.0.7.192/29 is exchanged with PE4 and shows up in PE4’s vrf table for Customer A (pending the RT is correct right?). So how do we get the 10.0.7.192/29 BGP network in the routing table and allow it to be known to the Customer A branch office router? If the CUST-A-BO router spoke BGP it would be easy but it doesn’t. So we end up having to redistribute the BGP information (routes with “B” in CUSTOMER_A vrf) into EIGRP. Take a look at the “redistribute bgp” command under the EIGRP process. On a side note, notice that the AS number for that vrf must be configured with the “autonomous-system” command (don’t forget that we could have multiple customers running EIGRP). So the main idea here is that we must redistribute from EIGRP into BGP then from BGP into EIGRP on the other side. Take a look at the vrf routing table on PE1 to see that you have both BGP and EIGRP routes.

Here is the routing table on the PE1 router (for Customer A networks):

Here is the routing table on the Customer A branch office router:

Stay tuned for OSPF PE-CE routing!

This entry was posted on Tuesday, April 24th, 2007 at 1:46 pm and is filed under Cisco, Routing&Switching. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.