I haven't seen all of the email on this subject, so forgive me
if this was all ready mentioned or if it "goes with out saying" but one
faily common case would be when a multi-homed customer prefers on provider
as primary and the other/s as a backup. The primary provider would prefer
customer announced routes over that of any peers, while the backup providers
would set there preferences to normal customers at highest, then peers, and
then the customer designated backup at lowest priority.
Absolutely. But then while primary is still up one would assume the (primary)
peer routes are preferred throughout the network of the backup provider
so it won't be announing anything anywhere (so nothing announced would
be inconsistent). I guess what I meant was "is there any case where a
customer would want a provider to prefer customer routes in some parts
of the provider net and peer routes elsewhere?".
To answer my own question:
One possible scenario for the above is if the customer had their own high
capacity ungongested East to West link, but couldn't get peering. Instead
the customer takes connectivity from two large providers, A and B, one
on the East and one on the West. As the large providers' backbones are
congested, the customer elects to do their own backhaul (may be they
are a content provider style customer and most of the high volume
traffic is outbound and handed off hot-potato). So if A and B have peer
routes which are a substantial % of the internet, and the A link is
West coast and the B East coast, the customer may prefer to get traffic
from A's East coast customers through B, rather than suffer a congested
backhaul through A. And vice-versa.
However I'd have thought the above scenario was relatively rare.