EIGRP is another protocol that can be used for CE-PE routing.


  • When staring the config make sure to always include the autonomous-system in address family, without that EIGRP neighbors won't form. This might be a hidden command in IOS, but no in IOS-XR.
  • Setting metric for BGP-> EIGRP redistribution is MIGHT BE requires depending on versions and platforms. Some versions require it, some don't.

MP-BGP Extended Community for EIGRP

  • BGP uses extended community to help PEs reconstruct EIGRP routes like the route type, source AS number, remote router ID and composite metric.
  • With these attributes, BGP carries enough information about the route to enable the router to converted back into EIGRP "transparently", just as if BGP had not been involved.
  • For the reconstruction of internal EIGPR route to occur, the destination AS must match the source AS carried by the BGP extended community.
  • If ASes are different routes will be considered external.
Type Usage Value
0x8800 General Route Info Flag:Tag
0x880l Reoute metric and AS AS:Delay
0x8802 Router metric Info Reliablity:HopCount:BW
0x8803 Router metric Info Reserver:Load:MTU
0x8804 External router info RemoteAS:RemoteID
0x8805 External router info RemoteProtocol:RemotMetric
  • Metric - composite metric of the EIGRP route.
  • Route Type - internal or external.
  • Source AS - AS specified in address family.
  • Remote Router ID - router ID
  • Cost Attributes - see Pre-Best Path section.

Pre-Best Path

  • EIGRP routes redistributed into MP-BGP are automatically tagged with BGP Cost Community. BGP Cost Community is an Extended Community which is checked before the Best-Path Selection Algorithm is calculated. This is used to allow MPLS VPN routes to be compared to internal EIGRP routes on the PE router.
  • In situation when a backdoor link exist with normal EIGRP to BGP redistribution behavior, the backdoor link would always win. That's because on each PE router, every locally redistributed route (backdoor EIGRP routes in this case) is given a weight value of 32768, while routes received from vpnv4 are not given any weight values.
  • A PE router having one route from a backdoor link and another one from the remote PE, would never consider the remote PE's route because it's never preferred in BGP (no weight assigned to it). This prevents CE routers of ever learning about paths coming from MPLS, paths that might have a better metric.
  • Command that disables pre-best path functionality is bgp bestpath cost-community ignore (it's a good way to test this functionality).
  • This is not required in SPF since all OSPF routes coming from the MPLS will be LSA type 3 and lose by design (unless an area is extened and sham links are used).
  • For more details go to BGP-Cost-Community.

EIGRP Site of Origin (SoO)

  • Mutual redistribution of protocols, especially with backdoor links, can cause routing loops. The usual method of resolving them is by using route-maps that match route tags, where a prefix is tagged as being redistributed and blocked from entering the same routing domain if it has the same tag. This could be a cumbersome solution to configure and track.
  • Site of Origin was introduced to simplify the redistribution loops.
  • The SoO extended community is a BGP extended community attribute that is used to identify routes that have originated from a site so that the re-advertisement of that prefix back to the source site can be prevented.
  • Two general rules of SoO processing:
    • If a route is sent or received on the same interface as the same SoO value was configured the route is discarded.
    • If a route sent or received on an interface that has an SoO value set, but it does not match the one configured for the interface, the value is preserved
  • To configure SoO for EIGRP, create a route-map that sets the extcommunity soo and apply it to an interface ip vrf sitemap (route-map). (in BGP you apply it per neighbor).


Relevant IOS Commands


Always include an as under address family.

R6(config-router-af)#        autonomous-system (as)

ip vrf sitemap

Sets a SOO route-map on an interface.

R1(config-if)#        ip vrf sitemap (rmap)

R1(config)#         route-map (name)
R1(config-rmap)#        set extcommunity soo (AS:nn)


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