[nsp] conditional BGP config - help

[Grant A. Kirkwood]

matthew zeier said:
>
>
>> On Mon, 22 Mar 2004, Pete Templin wrote:
>>
>> > matthew zeier wrote:
>> > > I have three transit providers - A, B, C - and want to setup
> conditional BGP
>> > > advertisements such that I only advertise my routes to C is both A
>> and
> B are
>> > > down.
>> >
>> > Alternate thought: advertise to C with several prepends (enough to get
>> > to nearly zero traffic) all the time, perhaps also with the
>> appropriate
>> > community (for provider C) to request peer-level local preference to
>> > minimize any reliance on the advertisement.  This way you can verify
>> the
>> > announcement at any time (i.e. through route-views.oregon-ix.net,
>> etc.)
>> > without having to wait for a double outage to test.
>>
>> A word of caution, minimise your prepends, try one, try two.. bad things
> can
>> happen when you overprepend your announcements, such as traffic
>> preferring
>> really bad paths during route leaks between peers etc
>
> One of my backup transit providers in turn buys transit from Aleron.  I'm
> trying to keep all traffic away from Aleron, however, certain broadband
> providers (Cox) appear to also get transit from Aleron.  Occassionally,
> Aleron appears to prefer my extra 10 AS prepends over my other upstream
> providers.


Of course... some providers will assign a higher local-pref to (for
example) peer routes, making your prepending (whether 1X or 10X)
completely irrelevant.

Grant


-- 
Grant A. Kirkwood - grant(at)tnarg.org
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