nanog mailing list archives

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


From: <alex () yuriev com>
Date: Tue, 10 Apr 2001 20:56:05 -0400 (EDT)


CEF should be called Customer Enrangement Feature. It is a very very very
bad idea to have linecards be anything else than forwarders. They
should not
make any intelligent routing decisions. There should not be a
tons of copies
of routing table on line cards.  That is what creates problems.

      CEF allows linecards to be forwarders. They don't make any routing
decisions, they just forward packets according to a routing table. (Routing
= deciding where packets should go, ie building a routing table. Forwarding
= sending packets to their destination, ie using a routing table.)

Excellent idea. Why, pray tell, then there is such things as "show cef
drop" and "show cef not-cef-switched"?

      The reality is that having only one copy of the routing table
creates an inevitable bottleneck.

Wrong answer. Routing table != forwarding table

For the same reasons this won't work on a regional network, it won't work
on a single router if the router is sufficiently complex.

Wrong answer again. Routing view != forwarding table

The same techniques that work to scale the Internet as a whole work inside
a box.

Wrong answer again. 
 
      Why do you think central fowarding is superior to distributed forwarding?

Because you will have consistency problem. You are nearly 100% guaranteed to
have them.

      DS

Alex



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