Any routing/network/BGP experts on the list?

[dsr-mzpnVDyJpH4k7aNtvndDlA at public.gmane.org (Dan Ritter)]

On Thu, Oct 14, 2010 at 12:04:40PM -0400, Matt Shields wrote:
> As the subject suggests, I'm looking for someone that's an
> routing/networking/BGP experts.
> 
> I have a question about BGP and AS Path Prepending.  I have 2 datacenters,
> each with their own ISP connection.  At both datacenters I have 2 routers
> that are connected to the ISP with VRRP.  To provide redundancy (automatic
> failover) to my main datacenter (everything is mirrored to my second one), I
> have configured BGP on all my routers so that the second datacenter prepends
> my AS 4x.  In theory, all traffic should go to my main datacenter because we
> do not do any prepending there.
> 
> To test this setup, we flipped the config so that we prepended 4x at the
> main datacenter and removed prepending at the secondary.  After hours of
> waiting traffic finally flipped over, but now when I change the prepending
> back to the default way and have been waiting hours it hasn't flipped back.
> Looking glass has shown the higher amount of prepends at the secondary
> datacenter, but still prefers the secondary one.
> 
> Last time I setup something like this was a few years ago and generally BGP
> updates happened fairly quickly within minutes across the net and routing
> was affected just as fast.  Anyone have any insight?


Are they both connected to the same ISP?  Are you testing from
multiple points? Are you advertising all your routes at both
locations? How many peers? Do the peers apply filters?
(Especially prefix-length filters?)

-dsr-

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