Subject: [Int-area] Some more feedback on draft-bonica-internet-icmp-08

From: Fernando Gont <[email-masked]>
Date: Tue, 26 Sep 2006 19:08:23 -0300

Folks,

A few more comments on the draft:

* While I don't expect the draft to list every possible use of the 
extensions, it might be good to add the motivation for these 
extensions. (a couple of lines, or a short paragraph)

* In several parts the draft talks about ICMP types, and includes in 
the same list "destination unreachable, parameter problem, etc.". 
However, "parameter problem" (and others) are *codes* of the same 
type ("destination unreachable"). This should be fixed.

* The header in Figure 1 includes a "Next-Hop MTU" field. However, 
this field is included only in "frag needed and DF bit set", but not 
for the other message codes.

* Page 5, section 4:
"   RFC 1191 [4] adds a "Next-Hop MTU" field to the Destination
    Unreachable message."

As explained in the previous bullet, RFC 1191 modifies only "frag 
needed and DF bit set"

* It might be a good idea to include the numerical type/codes for 
each of the messages, along with their "name".

Kindest regards,

--
Fernando Gont
e-mail: [email-masked] || [email-masked]
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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From: Carlos Pignataro <[email-masked]>
Date: Tue, 26 Sep 2006 22:48:50 -0400

Fernando,

Please see inline.

> type ("destination unreachable"). This should be fixed.

The only instance I found is:

      An ICMP Extension Structure MAY be appended to ICMPv4 Destination
      Unreachable, Time Exceeded, and Parameter Problem messages.

Are you referring to this one?

In any case, "Parameter problem" is ICMP Type 12 [RFC792] and a new code
(for this type) from [RFC1122], "Time Exceeded" is Type 11, and
"Destination Unreachable" is ICMP Type 3 (with >~ 13 codes).

> for the other message codes.

Yes; this is introduced in rev -07, since the text after figure 1 in -06 is:
   The syntax and semantics of all fields are unchanged from RFC 792 and
   RFC 1191.  However, a length attribute is added to the second word.

It should be fixed (as it was before, or somesuch adding that "Next-Hop
MTU" is only for "fragmentation needed and DF set")

Note that the underlying intent of the figure is to show the worst case
(for the type among all codes) field-usage-wise to place the length
field at a common offset.

> As explained in the previous bullet, RFC 1191 modifies only "frag 

Agreed. How about?

   RFC 1191 [4] adds a "Next-Hop MTU" field to the Destination
   Unreachable message with code indicating "fragmentation needed and DF
   set".

Thanks,

--Carlos.

-- 
--Carlos Pignataro.
Escalation RTP - cisco Systems

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From: Fernando Gont <[email-masked]>
Date: Wed, 27 Sep 2006 03:03:40 -0300

>"Destination Unreachable" is ICMP Type 3 (with >~ 13 codes).

Oops, sorry. For some reason I had in my head that time exceeded and 
others were different codes of "destination unreachable".
Forget this, then. :-)

>MTU" is only for "fragmentation needed and DF set")

Agreed.

>    Unreachable message with code indicating "fragmentation needed and DF

Good.

P.S.: Note that RFC 1812 (?) defines a whole bunch of ICMP messages 
(eg, "communication administratively forbidden..."). If the list in 
draft-bonica was meant to mention all ICMP messages, it should list 
those ones, too.

Kindest regards,

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From: Carlos Pignataro <[email-masked]>
Date: Wed, 27 Sep 2006 10:31:57 -0400

Fernando,

> draft-bonica was meant to mention all ICMP messages, it should list 

"Communication Administratively Prohibited" is code 13 for Destination
Unreachable type of 3 (like you say, from RFC1812); related codes for
the type are 9 and 10 from RFC1122.

Thanks,

--Carlos.