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Forum Replies

  1. 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

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  2. The default keepalive and holddown timer are 60 and 180 seconds (3x the keepalive):

    R1#show ip bgp neighbors | include keepalive
      Last read 00:00:20, last write 00:00:50, hold time is 180, keepalive interval is 60 seconds

    So what happens when you change these? For example, R1 uses a lower keepalive and holddown timer while (R2) uses the default:

    R1(config)#router bgp 1
    R1(config-router)#neighbor timers 10 30 

    The end result will be:

    R1#show ip bgp neighbors | include keepalive
      Last read 00:00:08, last write 00:00:08, hold time is 
    ... Continue reading in our forum

  3. Hi Rene,

    Do you have any idea how to use ASR 9010 capture BGP update message?
    The situation is:
    In topology: R1–SW1–SW2–R2,
    R1 and R2 has established BGP neighbor, and R1 can receive updates from R2,
    BUT, R2 cannot receive updates from R1.
    So, I’m trying to capture packet on R2 to see if the updates from R1 have been dropped.
    FYI, SW1 and SW2 are Layer 2 switch and are transparent in logically.

  4. Hi Chris,

    I took another look, this comes from the RFC 1771.

    The fourth high-order bit (bit 3) of the Attribute Flags octet is the Extended Length bit. It defines whether the Attribute Length is one octet (if set to 0) or two octets (if set to 1). Extended Length may be used only if the length of the attribute value is greater than 255 octets.

    The lower-order four bits of the Attribute Flags octet are unused. They must be zero (and must be ignored when received).

    The funny thing is, they removed the part about 255 octets from a later RFC (RFC 4271):

    The fou

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  5. Hello Dominique

    BGP by default will always advertise the single best path, for a particular destination, to its neighbours. There is a way to change this behaviour, and this is further discussed in the following lesson:


    A distance vect

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