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I would suspect that for the ICMP case, the IP ID wouldn't be too
useful for the transport and above layers as these layers typically
don't know (or care) about the ID in the IP header. <br>
<br>
Even for the retransmit cases, typically new IDs are used and no
attempt is made to reuse the ID with which the previously lost packet
was sent.<br>
<br>
Hoping that someone would clarify the purpose in life of the IP ID
field if the don't fragment bit is set. One answer that Jamshid Mahdavi
told me privately was that it would be useful at debugging time while
looking at packet traces.<br>
<br>
Thanks,<br>
<br>
S.R.<br>
<br>
David Borman wrote:<br>
<blockquote type="cite"
cite="mid200212131714.gBDHEBr05725@frantic.weston.bsdi.com">
<pre wrap="">Just a minor nit that I feel should be clarified:
</pre>
<blockquote type="cite">
<pre wrap="">From: der Mouse <a class="moz-txt-link-rfc2396E" href="mailto:mouse@Rodents.Montreal.QC.CA"><mouse@Rodents.Montreal.QC.CA></a>
Date: Fri, 13 Dec 2002 16:41:51 +0100 (CET)
Subject: Re: Question on "identification" field of IP header
</pre>
</blockquote>
<pre wrap=""><!---->...
</pre>
<blockquote type="cite">
<pre wrap="">Note that the portion of a packet returned in an ICMP does not include
even the IP source and destination addresses; the identification value
is almost the only value that can be relied upon to identify the
original packet upon getting an ICMP....
</pre>
</blockquote>
<pre wrap=""><!---->
Actually, ICMP packets are supposed to return the entire IP header
(including options) plus 64 bits of the IP data. So, you should get
up to the TCP and UDP port numbers. (RFC 792 explicitly states
that it assumes that higher level protocols have their port numbers
in the first 64 bits).
-David Borman
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</blockquote>
<br>
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