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Re: NSPs filter?

  • From: Jared Mauch
  • Date: Mon Aug 05 11:08:41 2002

On Sun, Aug 04, 2002 at 09:15:26PM -0700, Stephen Stuart wrote:
> > IMO, Commercial ISPs should never filter customer packets unless
> > specifically requested to do so by the customer, or in response to a
> > security/abuse incident.
> Let's say the customer operates some big enterprise network, runs
> their infrastructure in RFC1918 space ("for security," hah), and spews
> a couple kilobits of DNS query from that RFC1918 space toward the root
> nameservers. Assume that either pride or ignorance will prevent the
> customer from ever asking you to filter what you know to be garbage
> traffic. Does your rule to "never filter customer packets" mean you're
> going to sit and watch those packets go by?
> If yes, why?

	Everyone should turn on either the equivalent of
the Cisco 'ip verify unicast source reachable-via any' on their
peer/upstream interfaces as well as to internal and bgp customer
interfaces that may not be able to be checked with a stricter rpf.

	This will drop packets from people that you have no return
path for in the cef path.  I know other vendors either have or should
have this feature.  While it will not stem a true DoS based on real
ip addresses, zombies, whatnot.. it will stop all the rfc1918 headed
towards the roots or other space that is not in the global routing table.

	if your vendor doesn't have such a knob, i do suggest asking
them :)

	i've seen a lot of traffic get dropped by using such a
check on interfaces.  it is not a large amount compared to
the overall packets but does reduce what you end up transporting
and customer support queries about why 10.* is sending them packets.

	- jared

Jared Mauch  | pgp key available via finger from
clue++;      |  My statements are only mine.

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