Re: Last Call: <draft-ietf-intarea-ipv4-id-update-05.txt> (Updated Specification of the IPv4 ID Field) to Proposed Standard

Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp> Sun, 03 June 2012 19:13 UTC

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Date: Mon, 04 Jun 2012 04:12:30 +0900
From: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
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Subject: Re: Last Call: <draft-ietf-intarea-ipv4-id-update-05.txt> (Updated Specification of the IPv4 ID Field) to Proposed Standard
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C. M. Heard wrote:

>> Existing routers, which was relying on ID uniqueness of atomic
>> packets, are now broken when they fragment the atomic packets.
> 
> Such routers were always broken.  An atomic packet has DF=0 and any
> router fragmenting such a packet was and is non-compliant with
> the relevant specifications (RFCs 791, 1122, 1812).

Thank you. I have overlooked that atomic implied DF=1.

But, then,

   >> Sources emitting non-atomic datagrams MUST NOT repeat IPv4 ID
   values within one MSL for a given source address/destination
   address/protocol triple.

makes most, if not all, IPv4 hosts non compliant if MSL=2min.

Worse, without hard value of MSL, it is a meaningless
requirement. Note that MSL=2min derived from RFC793 breaks
150Mbps TCP.

The proper solution, IMHO, to the ID uniqueness is to request
a destination host drop fragments from a source host after
it receives tens (or hundreds) of packets with different IDs
from the same source host.

A source host, then, is only required to remember the
previous ID used for each destination.

						Masataka Ohta