Subject: Re: [MBONED] Handling NAT

From: "SAYKO, ROBERT J (ATTSI)" <[email-masked]>
Date: Wed, 16 Mar 2011 14:47:48 -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:
-Network Address Translation is not specifically considered in the draft
-With NAT, multiple GWs may attempt to establish tunnels using the same
external source IP address
-Some types of NAT devices (Symmetric NAT) may use different external
source ports  depending on the destination address
-Therefore, GW messages to the Relay Anycast address (Discovery) and
messages to the Relay unicast address (AMT Request and AMT Update) may
arrive with different source ports from a single GW.

Recommendation:
-Relay must track GWs using both Source IP address and Source Port
-AMT GW should use the same local source port for all its messages to
the Relay (especially all 3-way handshake messages)
-Relay should start tunnel only with the 3-way handshake (not Discovery)

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