[c-nsp] eBGP & backup static route

[Tim Franklin]

On Tue, February 17, 2009 4:16 pm, Saku Ytti wrote:

> Only thing setting weight 0 on the backup does, is makes sure that
> also local traffic behind backup PE, starts to flow via primary,
> instead of choosing the local backup route.

And also forces the backup PE to consider the primary route in his BGP
best-path selection.  If you leave the weight as 32768, the backup PE will
always select the redist-from-static route as the best path, and announce
it to the network, which means you still have to play with other knobs to
make sure the rest of the network picks the primary route (and you're
wasting resource sending the route around / forcing all the other boxes to
make that decision).

Weight 0 lets you contain the route on the backup PE (by decreased
localpref, increased localpref on the primary, whatever other magic) and
never announce it to other BGP speakers.

> If it is indeed same box (ouch, backup and primary in same box,
> I hope not) then resetting weight is needed.

Or if your PE split is on access-type rather than just role.  "DSL PE" is
common - if this site has DSL backup, but other sites in the VPN are DSL
primary, you can get the smaller sites all using the backup connection of
the larger site.

Regards,
Tim.