I must respectfully disagree: better in my opinion is
to receive partial routes from multiple providers
(specifically, the providers' own routes), and then
keep a default route to your least-used provider. If
you discover that some particular address isn't
reachable, direct the traffic elsewhere. The real
solution is to pay attention, and make sure that
you're aware of what your providers are doing: peering
loss between providers isn't nearly as bad as complete
business failure, although they can both be as deadly.
You are fixing the example, rather than the problem.
My contention is that it's substantially more
effective (both in terms of cost and results) to use
human intervention to resolve this type of problem
rather than rely on an automatic system. There were
warnings before the whole C&W/PSI fiasco, and this
seems to be the rule rather than the exception.
For the C&W/PSI fiasco, yes. For other types of connectivity losses,
probably not. Some may only last for a few hours, by the time you respond,
the problem is over.
Without full routes from at least one provider, how can you tell what
traffic is affected by the fiasco even if you know about it? You often can't
just take customer routes and point default away from a link with a problem
like that because so much traffic takes the default route that your other
link(s) would be too heavily loaded. (Of course, if your providers are
large, this is less of a problem since customer routes will cover more of
Wven having full routes won't help you when your provider sends you routes
it can't actually handle traffic for. Sometimes, a sick router is too sick
to withdraw routes, but it can still take an awfully long time for the BGP
session(s) to it to break.
If you have a lot of delay-sensitive traffic, taking full routes can also
result in a performance improvement. Also, taking shorter routes generally
means taking more reliable routes as there are fewer points for there to be
problems that might not be reflected in the BGP routes (like a sick router,
overloaded link, or misconfigured filter).
I wasn't trying to start an argument about how to deal with peering fights,
really. I was just trying to voice the other side of the 'no need to take
full routes' fight.