I'm sitting here writing a new as-path access-list for a peer, and a
question popped into my head:
Is there any reference that gives some idea of the processor overhead of a
given regular expression operand? In particular, if I do
as-path access-list 1 permit ^100_((200|300|400|500)_)*$
on the command line, it seems a lot faster than
as-path access-list 1 permit ^100_((200|300|400|500)_)+$
(which requires at least one instance of 200, 300, 400, or 500 in the path
for a match). This all makes sense, of course, but I am curious how much
of a performance penalty is incurred when a + or [] are used to whittle
down path matches. An additional question (perhaps more relevant to the
real world) is whether:
permit ^100_200$
permit ^100_300$
permit ^100_400$
is any faster than:
permit ^100_(200$|300$|400$)
or
permit ^100_(200|300|400)$
Any pointers of guesses appreciated.
Thanks.
-travis
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