BGP and IGP stuff

Discussion in 'Cisco' started by Sam Wilson, Feb 21, 2007.

  1. Sam Wilson

    Sam Wilson Guest

    This may be a very stupid question, for which please forgive me. I've
    been running BGP for 10+years and I've never had to think about this
    before.

    We run a metropolitan network which uses eBGP with a private AS for each
    site. (The appropriateness of eBGP is a discussion for another day,
    thank you.) There may be static routes or an IGP (OSPF) for
    distributing routes into BGP at the site. We have recently started
    installing backup links for some of the connections within a site and
    obviously the IGP just sorts that out.

    What would be nice would be to land a back up link from one site into a
    router in a different AS. Network N, say, normally announced in AS X
    would now also need to be announced by AS Y. I don't really want to run
    BGP on the backup link. Is this possible? Would things get confused if
    N appeared in both ASs? We'd need to pad the announcement from Y to
    make sure the backup wasn't used in normal traffic (it's lower bandwidth
    and intended only for emergencies). Should we pad the AS path with Xs
    or Ys or both? Padding with Xs would make N appear to be in X, but is
    that sensible or possible?

    Or is this just a really stupid idea? :)

    Thanks,

    Sam
     
    Sam Wilson, Feb 21, 2007
    #1
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  2. On 21.02.2007 16:27 Sam Wilson wrote

    > This may be a very stupid question, for which please forgive me.
    > I've been running BGP for 10+years and I've never had to think about
    > this before.
    >
    > We run a metropolitan network which uses eBGP with a private AS for
    > each site. (The appropriateness of eBGP is a discussion for another
    > day, thank you.) There may be static routes or an IGP (OSPF) for
    > distributing routes into BGP at the site. We have recently started
    > installing backup links for some of the connections within a site and
    > obviously the IGP just sorts that out.
    >
    > What would be nice would be to land a back up link from one site into
    > a router in a different AS. Network N, say, normally announced in AS
    > X would now also need to be announced by AS Y.


    why that. Until now I've not seen any good reason to ever have any
    prefix in two different AS.

    > I don't really want to run BGP on the backup link.


    why not?

    > Is this possible? Would things get confused if N appeared in both
    > ASs? We'd need to pad the announcement from Y to make sure the
    > backup wasn't used in normal traffic (it's lower bandwidth and
    > intended only for emergencies). Should we pad the AS path with Xs or
    > Ys or both? Padding with Xs would make N appear to be in X, but is
    > that sensible or possible?
    >


    I would run BGP on the backup links and prepend appropriately. That
    should do the trick.




    Arnold
    --
    Arnold Nipper, AN45
     
    Arnold Nipper, Feb 21, 2007
    #2
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  3. Sam Wilson

    Sam Wilson Guest

    In article <>,
    Arnold Nipper <> wrote:

    > On 21.02.2007 16:27 Sam Wilson wrote
    >
    > > I don't really want to run BGP on the backup link.

    >
    > why not?


    Because it would mean changing my nice neat mental model. :) (Which,
    of course, is getting un-neat...)

    > I would run BGP on the backup links and prepend appropriately. That
    > should do the trick.


    Yeah - I'll think about that some more.

    Sam
     
    Sam Wilson, Feb 22, 2007
    #3
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