gigabit router (was Re: Getting a "portable" /19 or /20)

I used to give a course on building high speed routers. A section of the
course was entitled "common mistakes to avoid." One of them was precisely
this problem. The rule is forward once within a box -- if linecard X has
decided how a packet is to be forwarded, linecard Y shouldn't be reconsidering
the decision. (And, in fact, if you look at most linecard designs, the
output path, from switch to transmission, does not include a forwarding
engine -- there's only a forwarding engine on the inbound path).