You're right you don't need a default route. However, imagine
that you don't have confidence in the routing table entries.
Imagine a situation like this:
Imagine that you take full routing tables from NSP1e. There is a
bit of latency in him getting a route propogated, so conceivably
with some flapping issues, you might not have it if you wanted it.
So, what you could do is default to NSP1e. If you're multihomed,
Concievably you could have wacky problems at 'you' which could
cause you to drop packets. By having a default, you entrusted the
delivery in those situations to one of your upstreams.
ps. we multihome to 2 providers, we take full routing tables, and
we don't have an external default. I'm not recommending the above
logic, just expounding on a possible explanation.....
......... David ``Joel Katz'' Schwartz is rumored to have said:
] On Mon, 8 Apr 1996, Avi Freedman wrote:
] > Now, many 2nd level providers that *could* operate default-free choose
] > not to. Even if you have three or more sets of 30k+ routes each, it
] > takes balls to risk dropping packets that your customers want you to
] > deliver just so that you can have the packet be dropped at your router
] > instead of at your (possibly backup) transit provider's router.
] > Avi
] Can't anyone who takes full routes from any tier 1 provider
] operate without a default route? And isn't it a reasonable assumption
] that if you don't have a route somewhere, odds are they don't have a
] route to you (assuming you do your own BGP routing) and so a default
] route is mostly pointless anyway?
] What am I missing?