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Forum Replies

  1. Hi Hamood,

    GNS3 makes this really simple. You can right-click on any interface and select “capture”. It will automatically start Wireshark and show you the traffic that flows through the link.


  2. Rene,

    In the capture which you gave for EBGP adjacency have seen two update messages , can you explain when will we have to BGP UPDATE messages.


  3. Hi Dhanu,

    The second update message is empty and is used to indicate that all routes have been sent. You can read more about it in RFC4724:

    An UPDATE message with no reachable Network Layer Reachability Information (NLRI) and empty withdrawn NLRI is specified as the End-of-RIB marker that can be used by a BGP speaker to indicate to its peer the completion of the initial routing update after the session is established.


  4. Hello Rene,
    I have couple of questions regarding the timers used in BGP. Correct me if I am wrong. Bgp uses keepalive of 60 seconds and hold down timer of 180 seconds by default. So here the keepalive works like hello messages like in ospf and hold down timer works like dead timer in ospf. Am I correct? Let’s say Router A is peering with Router B by EBGP and router A is using keepalive of 60 seconds and hold down timer of 180 seconds whereas Router B is using keepalive of 100 seconds and hold down timer of 300 seconds. In this case, what would be the negotiated keepalive and hold down timer that both routers will use? My second question. Let’s say Router A is peering with Router B by EBGP and and Route-maps are in place for filtering in both routers. In this scenario, if I make any change in the outbound route-map assigned to Router A and do not run clear ip bgp * soft, how long is it going to take Router B to get the update? How long does it take a router to get the update when any route goes down in the neighboring AS router? Thank you in advance.

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