Subject: [BEHAVE] about CGN requirements (1)

From: Francis Dupont <[email-masked]>
Date: Sat, 26 Mar 2011 21:46:42 +0100

This is the first of a serie of comments about CGN requirements
(aka draft-ietf-behave-lsn-requirements-01.txt).

1 page 3: quoting
  "This document builds upon previous works describing requirements for
   generic NAT devices.[RFC4787][RFC5382][RFC5508].  These documents
   still apply in this context.  What follows are additional
   requirements, to be satisfied on top of previous ones."

=> even if I understand what the CGN requirements should build on the
previous NAT RFCs I am afraid this makes the document to inherit very
questionable ("disconnected from the reality" to stay polite)
requirements like RFC 5382 REQ-5:
 "established connection idle-timeout" MUST NOT be less than 2 hours
 4 minutes.
or even RFC 4787 REQ-1:
 A NAT MUST have an "Endpoint-Independent Mapping" behavior.
because:
 - ~70 % of deployed NATs don't implement EIM (i.e., this requirement
  is simply ignored in the real world)
 - this doesn't seem to have a negative impact on users (i.e., the reasons
  of this requirement doesn't match the real world)
 - as far as I know ISPs want strong port randomization (i.e., something
  which is opposed to efficient sharing scheme as EIM)
Note I don't argue EIM is silly, it is a fine way to improve port sharing
(the function of NATs) but the MUST is clearly not appropriate for CGNs.

Regards

[email-masked]