Subject: (ngtrans) shipworm: interval determination procedure

From: Erik Nordmark <[email-masked]>
Date: Thu, 24 Jan 2002 11:54:57 +0100 (CET)

I have a concern about the robustness of:
4.2.6	Optional Refresh Interval Determination Procedure 

The unstated assumptions are that the lifetime of the UDP NAT mapping
is 
 - constant over time
 - independent of other traffic through the NAT box
 - and perhaps others

Turns out that the NAT box I have at home violates the second of the above
assumptions. It is a combined router/NAT/ISDN modem.
The observed behavior is that the UDP mapping is discarded when the ISDN
call is dropped (after 2 minutes of no traffic) but if there is traffic
that keep the ISDN call up then the UDP mapping lives for between 6-20 minutes
(even when there is no traffic using that UDP mapping).

Using the interval determination procedure with such a NAT box
would have the effect that if there is other traffic through the NAT box
(e.g. using shipworm or TCP/IPv4 traffic) the interval could be determined
to be too large, which will result in not being able to maintain the 
IPv6 address once the other traffic is not present.

What are the benefits of the interval determination procedure?
Are they worth the above type of failure mode?

  Erik