Subject: Benoit Claise's Discuss on draft-ietf-6man-rfc1981bis-06: (with DISCUSS and COMMENT)

From: Benoit Claise <[email-masked]>
Date: Thu, 11 May 2017 03:45:38 -0700

Benoit Claise has entered the following ballot position for
draft-ietf-6man-rfc1981bis-06: Discuss

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DISCUSS:
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  Nodes not implementing Path MTU Discovery MUST use the IPv6 minimum
   link MTU defined in [I-D.ietf-6man-rfc2460bis] as the maximum packet
   size. 

I searched for "IPv6 minimum link MTU" in draft-ietf-6man-rfc2460bis-09,
and could not find that term.
Even unlikely at this point in the IPv6 implementation cycle, we don't
want readers to believe that they should look at the minimum of the
device IPv6 MTU link(s).
Proposal: define "IPv6 minimum link MTU" as 1280 octets in 2460bis, or in
both documents.

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COMMENT:
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In this document, I see:

   IPv6 nodes SHOULD implement Path MTU Discovery in order to discover
   and take advantage of paths with PMTU greater than the IPv6 minimum
   link MTU [I-D.ietf-6man-rfc2460bis].  A minimal IPv6 implementation
   (e.g., in a boot ROM) may choose to omit implementation of Path MTU
   Discovery.

In draft-ietf-6man-rfc2460bis-09:
   It is strongly recommended that IPv6 nodes implement Path MTU
   Discovery [RFC1981], in order to discover and take advantage of path
   MTUs greater than 1280 octets.  However, a minimal IPv6
   implementation (e.g., in a boot ROM) may simply restrict itself to
   sending packets no larger than 1280 octets, and omit implementation
   of Path MTU Discovery.

So a SHOULD in one document versus "strongly recommended" in the other.

We should reconcile the two texts.
Note: may and may are consistent.

ICMPv6 PTB => ICMPv6 Packet to Big (PTB)

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From: Fernando Gont <[email-masked]>
Date: Fri, 12 May 2017 05:26:45 +0200

> https://datatracker.ietf.org/doc/draft-ietf-6man-rfc1981bis/

Well.. isn't SHOULD == RECOMMENDED in RFC2119-speak?

Cheers,
-- 
Fernando Gont
SI6 Networks
e-mail: [email-masked]
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492

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From: Benoit Claise <[email-masked]>
Date: Fri, 12 May 2017 11:27:05 +0200

> Well.. isn't SHOULD == RECOMMENDED in RFC2119-speak?
Yes, but SHOULD <> "strongly recommended"
Just be consistent.

Regards, Benoit

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From: Bob Hinden <[email-masked]>
Date: Fri, 12 May 2017 14:16:11 -0700

Benoit,

Comments below on your Discuss.

Bob

> On May 11, 2017, at 3:45 AM, Benoit Claise <[email-masked]> wrote:
> 

The text in rfc2460bis (unchanged from rfc2460) is:

5.  Packet Size Issues

   IPv6 requires that every link in the internet have an MTU of 1280
   octets or greater.  On any link that cannot convey a 1280-octet
   packet in one piece, link-specific fragmentation and reassembly must
   be provided at a layer below IPv6.

   Links that have a configurable MTU (for example, PPP links [RFC1661])
   must be configured to have an MTU of at least 1280 octets; it is
   recommended that they be configured with an MTU of 1500 octets or
   greater, to accommodate possible encapsulations (i.e., tunneling)
   without incurring IPv6-layer fragmentation.

rfc1981bis (and rfc1981) doesn’t use "IPv6 minimum link MTU” as a defined term (otherwise it would be in Section 2. “Terminology”.  It’s just words describing the concept in Section 5 of rfc2460bis (as shown above).

> Proposal: define "IPv6 minimum link MTU" as 1280 octets in 2460bis, or in

I think rfc1981bis (and rfc1981) are correct about pointing to rfc2460bis (and rfc2460).  Having to change it in two places would make it much harder to change it in the future.

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From: Benoit Claise <[email-masked]>
Date: Wed, 17 May 2017 06:01:27 -0400

Hi Bob,
> I think rfc1981bis (and rfc1981) are correct about pointing to rfc2460bis (and rfc2460).  Having to change it in two places would make it much harder to change it in the future.
So the term "IPv6 minimum link MTU" is being added in 
draft-ietf-6man-rfc2460bis, right?
I don't see it in the version posted yesterday.

Regards, B.