BGP route reflector details

BGP route reflectors have been supported in Cisco IOS well before I started to develop the first BGP course for Cisco more than a decade ago (one of the early ABCT course descriptions is still available online thanks to the Wayback machine). It’s a very simple feature, so I was pleasantly surprised when I started digging into it and discovered a few rarely known details. Read all about the BGP route reflector details in the article I wrote in the CT3 wiki.

7 comments:

  1. Hi Ivan,

    Referering to this article "http://wiki.nil.com/BGP_route_reflectors" can you please confirm if this statement that has been specified in the "Route Reflector Rules Section" is actually true.

    "An IBGP route received from a route-reflector client is sent to all IBGP peers, including the client from which it was received."

    I tried researching this a bit as I was curious and no other discussion has explicitly stated that the route is reflected back to the client from which it was received. Infact this would actually go against the split horizon rule. The RFC doesn't mention of this either (Atleast I couldn't find it in the RFC:-)

    Please could you confirm. Thx for help.

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  2. The statement you've quoted is a direct result of Section 6 of RFC 4456. You can find the in-depth details in BGP Route Reflector update groups (technical details) article.

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  3. Hi Ivan,

    Which community will be sent if only "neighbor {ip-address} send-community" is configured?

    Thanks, Pete

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  4. The "neighbor send-community" enables the community propagation.

    Without this option, no communities will be sent to the BGP neighbor, after it has been configured, the router will propagate communities attached to BGP entries in its BGP table to the neighbor.

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  5. I meant standard, extended or both communities are sent by default, if only the "neighbor send-community" is added wihout any option [both | standard | extended].

    http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp3.html#wp1016586

    Thanks, Pete

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  6. @Anonymous Pete: Standard only (at least the last time I've checked). Do you see something else?

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  7. I am running MP-BGP with RR in network and I have problem with Aggregated route propagation through RR. Client sends update to RR, RR installs route in routing table but doesn't send it to other clients..

    Aggregation is done using

    aggregate-address prefix mask summary-only

    Does anybody know anything about this??? Thanks

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.