Subject: [Ietf-behave] Issue 6 - ICMP draft issues from the IETF 65 WG meeting

From: Pyda Srisuresh <[email-masked]>
Date: Sat, 24 Jun 2006 07:35:02 -0700 (PDT)

ISSUE-6:

  6. DF behavior, follows normal router behavior.  Question:  keep
  this in the draft, or pull it out.  

  Lars suggested that RFC1812 should be the baseline here - "NATs
  should look like routers".  And that instead of duplicating what
  RFC1812 says, just point out the differences from RFC1812.

RESOLUTION: REQ-8 of the ICMP draft reflects the above consensus as follows.

   REQ-8: A NAT device MUST conform to RFC 1812 in IP packet handling.
   Below are specific instances where a NAT device MUST conform to 
   RFC 1812.
   a) If DF bit is set on a transit IP packet and the NAT
   device cannot forward the packet without fragmentation, the
   NAT device MUST send a "Packet too big" ICMP message (ICMP
   type 3, Code 4) with a suggested MTU back to the sender and
   drop the original IP packet.
   b) A NAT device  MUST, by default, generate "Time Exceeded" ICMP
   error message when it discards a packet due to an expired TTL field,
   unless explicitly configured otherwise.