Subject: [RPSEC] Use and semantics of AS_PATH, etc

From: Tony Tauber <[email-masked]>
Date: Tue, 1 Feb 2005 15:35:05 -0500

Taking off from some discussion on and off the list, I'd like to hear,
hopefully from the operational community directly, how various
components w/in BGP are used.  For instance, Alex Zinin suggested to
me some questions and elaboration for which I think "AS_PATH" could be
replaced also by "Communities", for instance:

++>   1. Exactly why people want secure AS_PATH
++>   2. How AS_PATH can be secured
++>   3. What exactly secured AS_PATH gives us
++>
++> Point 1 should go beyond "this is how BGP works", since BGP
++> mechanisms (like putting local ASn in the AS_PATH) are the means
++> of achieving certain protocol behavior (e.g. loop-freeness) and
++> information collection (e.g. for debugging flapping routes),
++> rather then self-contained objectives. In other words, BGP is not
++> a route propagation tracking tool.
++>
++> Point 2 should give us the answer on what type of security
++> mechanisms are applicable to the AS_PATH given how BGP speakers
++> manipulate this attribute.  E.g., signing at each BGP peer, or
++> whether we can secure ASn deletion, etc.
++>
++> Point 3 should answer the question "ok, the AS_PATH I received
++> passed the security check, what can I tell based on this now?".
++> Part of it will be analyzing how AS_PATH security plays together
++> with the basic BGP behavior.  Finally, we should be able to go
++> back to question 1 and say if we can satisfy those requirements.

My hope (and Alex's, I think) is to stimulate thought and discussion
about:

 - How these things are used
 - How they could be abused
 - The costs of mitigating those risks

Discuss.

Tony

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