I was at a meeting talking to ops people from some large ISPs, who tell me
that when they tell their large customers about BCP 38, the customers say
forget it, because they're multihomed. I gather the situation is
typically that the customer has multiple address ranges, say from
providers A and B. Normally traffic from range A goes out through
provider A, and vice-versa, except sometimes when it doesn't. Sometimes
it's failover, or it may be deliberate asymmetic routing. The customers
may not be running BGP, or if they do, they don't want to announce range A
to provider B for business reasons I don't entirely understand but that
are not going away.
The ISPs tell me that the customers are often ISPs themselves, so there
are lots of address ranges, far more than anyone could track manually even
if they wanted to.
I see BCP 84, which is now ten years old. The ISPs are aware of it, but
it doesn't seem to have done the trick. I can think of some hacks to
pseudo-announce ranges for filtering purposes, but surely I am not the
only person to have noticed this problem. What have people done to
address this issue?* I figure the first thing to do is to understand
what's failed before.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail.
* - other than calling the customers stupid, which they are not, and is
not helpful