Great Suggestion for the DNS problem...?

Alex Pilosov alex at
Thu Aug 28 21:26:14 CDT 2008

On Thu, 28 Aug 2008, Brian Dickson wrote:

> However, if *AS-path* filtering is done based on IRR data, specifically
> on the as-sets of customers and customers' customers etc., then the
> attack *can* be prevented.
> The as-path prepending depends on upstreams and their peers accepting
> the prefix with a path which differs from the expected path (if the
> upstreams register their as-sets in the IRR).
You are thinking about this specific exploit - which may in fact be
stopped by as-path-filtering. However, that's not the problem you are
solving. Problem is the hijacking. There are many other ways to reinject
traffic closer to victim - will require attacker to work a little harder,
but not really fix the problem. (Think, GRE tunnels, no-export,
no-export-to-specific-peer, etc).


> So, if the upstreams of as-hijacker reject all prefixes with an as-path
> which includes as-bar (because as-bar is not a member of any customer's
> as-set expansion), the attack fails.
What's to stop me from adding as-bar into my as-set? To do what you are
describing, you will have to enforce "export AS-LEFT" and "import
AS-RIGHT" rules on every pair of AS-PATH adjacencies. And I'm not sure if
existing tools can do that - or how many existing adjacencies fail that

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