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North American Network Operators Group

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Re: router worms and International Infrastructure

  • From: Matthew Crocker
  • Date: Thu Sep 22 08:53:54 2005

At your borders (upstream/peers), you will naturally block all of 10/8
at egress.

my border is very broad and it's not feasible to use acls on all equipment
that makes up that edge :( (for the sake of arguement, which is now far
afield from the original question: "Feasible path won't stop someone
spoofing space thats in my FIB, will it?"

The solution is a double border, possibly with VRF and inter-VRF routing

Internal border sees 10/8 and 10/8 is in the FIB. 10/8 packets can be spoofed here, Infrastructure connects her
External border doesn't see 10/8, 10/8 is NOT in the FIB, 10/8 packets can't be spoofed. Internet connects here.

Internal <-> External links use routable IP space to not infect external with infrastructure routes.
External border cannot talk to infrastructure IPs but it doesn't need to.
External can route through infrastructure to customer CPE

10/8 can still be spoofed on the infrastructure but it will have to come from a customer, not from the Internet.

Also, consider the cases where customers push packets your way (for uRPF
strict, which isn't available for JunOS, but is for IOS depending on
platform/code/hardware-rev... ugh!) and never send you a route for the
traffic back to them? Maybe they are just a transit and don't even hear
the routes for their customer who chose a 'cheaper' path that doesn't
include them nor me directly on this link in question?

This sounds like a broken design. Why have one way links? If a customer pushes packets my way and they don't announce that route to me I will drop the packets at my edge. If they want to send me those packets they need to announce. They can announce with AS path prepend x 1000 so I don't send them any traffic but the route needs to exist.

"does urpf feasible path stop a 'customer' from spoofing sources that are
in the FIB?"
No, but you don't use feasible path on links aimed at your customer, you use strict. If your router doesn't support strict then talk to your purchasing department.

Matthew S. Crocker
Vice President
Crocker Communications, Inc.
Internet Division
PO BOX 710
Greenfield, MA 01302-0710

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