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Re: Who does source address validation? (was Re: what's that smel l?)

  • From: Hank Nussbacher
  • Date: Thu Oct 10 09:15:47 2002 
At 10:43 PM 09-10-02 -0700, Steve Francis wrote:


[email protected] wrote:

My personal pet peeve is the opposite - we'll try to use pMTU, some
provider
along the way sees fit to run it through a tunnel, so the MTU there is
1460
instead of 1500 - and the chuckleheads number the tunnel endpoints out
of
1918 space - so the 'ICMP Frag Needed' gets tossed at our border
routers,
because we do both ingress and egress filtering.
That's not terribly hard to overcome - allow icmp unreachables (from any source) in your acl, then deny all traffic from RFC 1918 addresses, then the rest of the ACL.

Combined with CAR (or CatOS QoS rate limiting) on icmp's, you end up with all the functionality, and almost none of the bogus traffic.
CAR should not be used to rate-limit but instead use the MQC police command
which basically does the same thing. CAR is not going to be around much longer and is not being developed anymore:

Have a look at:
http://www.cisco.com/warp/public/105/cbpcar.html
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_c/fqcprt8/qcfmcli2.htm
for more information.

-Hank