The reason we (as an operator) can’t use BCP-38 is the vendor hardware can’t
do it at line-rate and
the performance hit is too much to sustain.
A year or two ago I was talking to some largish providers who told me
that their problem was multihomed customers who have PA space from
multiple providers and for varions reasons (not all silly ones) don't
always send traffic to the port corresponding to the address. The
usual customer response when asked to clean up their routing is "if
you don't want our $<large> per month, we're sure we can find other
providers that do."
This strikes as a problem that could be solved by providing some way
for routers that don't do BGP to tell their upstreams what the other
address ranges are, but of course the real issue is whether such a
hack could get implemented in routers that people actually buy and
use.
R's,
John