AS for inter-AS link subnets?

Discussion in 'Cisco' started by Sam Wilson, Apr 17, 2007.

  1. Sam Wilson

    Sam Wilson Guest

    In BGP what AS should the link subnet between eBGP peers be announced
    in? Is it OK to announce it separately in each AS? If not what else
    can one do?

    Sam Wilson, Apr 17, 2007
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  2. Sam Wilson

    Sam Wilson Guest

    Hi Lars,
    thanks for the response. It doesn't help much, but I expect it's
    because I left out the detail.

    We use eBGP with private ASs. The subnets linking the ASs are not
    naturally part of any of the ASs and they are not currently announced.
    This has some niggling problems we'd like not to have. Consider a
    triangle of ASs, call them X, Y and Z. If the link between X and Y goes
    down then normal traffic between X and Y works just fine via Z, but the
    border routers in X and Y can't do simple debugging things to each other
    because they source traffic from the interfaces addresses of the X-Z and
    Y-Z links which aren't announced to Y and X respectively. Clearly you
    can specify the source addresses for the debugging commands to be, say,
    the loopback addresses of the routers, but you have to remember and it
    confuses people. :)

    So if we want to announce the inter-AS link subnets can we do it from
    both ASs or is there something else we should be doing?
    Sam Wilson, Apr 17, 2007
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  3. Hi Sam

    You could choose not to announce the link at all, but normally the "owner"
    (the AS) who has the IP adresses assigned is the one to announce these IP
    adresses in the normal aggregation.

    Hope this helps.

    Regards, Lars
    Lars L. Christensen, Apr 17, 2007
  4. Sam Wilson

    Merv Guest

    Assuming that the the interfaces connecting the AS's are advertised
    withing their respect IGP's, I do not see any reason for you to be
    able to annouce the "DMZ" links via EBGP.
    Merv, Apr 17, 2007
  5. Sam Wilson

    Merv Guest

    Merv, Apr 17, 2007
  6. Sam Wilson

    Sam Wilson Guest

    "... not to be able ..."?

    Sam Wilson, Apr 18, 2007
  7. Sam Wilson

    Merv Guest

    yes, sorry for the typo
    Merv, Apr 18, 2007
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