Subject: Re: [MBONED] When to do Discovery?

From: "SAYKO, ROBERT J (ATTSI)" <[email-masked]>
Date: Wed, 16 Mar 2011 14:49:21 -0400

At AT&T base on our experience,  testing and investigation we would like
to present the following recommendation as an addition to the
"Automatic IP Multicast Without Explicit Tunnels
(AMT)draft-ietf-mboned-auto-multicast-10"

Problem:
-Current AMT draft is ambiguous on when the AMT GW should do Discovery
	>Mentions both that it could do at startup and also that it
should do to establish tunnel
	>Periodic refresh (e.g. every 24 hours) of Discovery is also
mentioned
-Doing Discovery only at startup has issue that network/Relay conditions
could change over time - thus, the "best" Relay 
 available may have changed between startup and 1st join
-Doing periodic Discovery may have performance considerations when
changing Relays mid-stream
-If the AMT Relay uses the Discovery to reserve resources, it is
susceptible to DoS attacks using Discovery

Recommendation:
-Clarify draft to be specific that a Discovery is recommended by the AMT
GW just prior to the start of each tunnel
-However, the Relay should not use the Discovery to establish the tunnel
due to Symmetric NAT issue and DoS issue.   It 
 should establish tunnel at the 1st successful join from GW
-Periodic Discovery should be an option left as implementation issue.
If changing Relays mid-stream, GW may use the 
 Teardown message to clean up tunnel at "old" Relay

Robert Sayko
AT&T Labs
732-420-3292
[email-masked]