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Any way can I figure out what policy allows a prefix on the BGP remote side ?

  • 1.  Any way can I figure out what policy allows a prefix on the BGP remote side ?

    Posted 12-05-2020 12:22
    If the remote side does not tell what Prefix is allowed on its side ?  Can I find out ?

    For example, the remote side only allows 192.168.0.0/16,  but I advertise 192.168.0.2.  then rejected by the remote side. How can I know the remote side only accepts 192.168.0.0/16 ?

    thanks in advance !!


  • 2.  RE: Any way can I figure out what policy allows a prefix on the BGP remote side ?

     
    Posted 12-05-2020 12:36
    The simple answer is: If your service with the IP address 192.168.0.2 is reachable from the outside, or more generally the service behind this IP address works fine, then it is accepted by the remote side.

    But there is no "tell the BGP neighbor which IPs I accept or do not accept knob". If the remote side does not accept this announced prefix, then it is just discarded, nothing else.

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  • 3.  RE: Any way can I figure out what policy allows a prefix on the BGP remote side ?

    Posted 12-05-2020 12:47
    thanks !!
    I am not sure whether I should ask this or not here.
    The reason I asked is I am taking Juniper JNCIE training, the lab asks to establish eBGP to the ISP, but the lab does not tell you any information related to ISP BGP.  I can use sniff and traceoptions to find AS and peer IP, but when I advertise 192.168.0.2,  it does not work. It only accepts aggregate 192.168.0.0/16.  So I am wondering some tricks here which I do not know.