Any routing/network/BGP experts on the list?

[Matt Shields]

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?

-matt