Re: [Last-Call] [EXTERNAL] Re: Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC

"Templin (US), Fred L" <Fred.L.Templin@xxxxxxxxxx> · Thu, 3 Feb 2022 22:13:15 +0000

Hi Joe,

> Why stop at 32 bits? They COULD expand to 128. Or 1024. Or more.

RFC4443 PTB stops at 32 bits and RFC2675 Jumbo Payload stops at 32bits.
So should this.

> If and when we ever get close to 64K, we could easily declare all 1’s as indicating the need for an extended value

IP parcels give a reason for link MTUs > 64K, and link designers will start to take note.

> IMO, let’s not complicate things unnecessarily now.

I understand, but the problem is this document is reserving one of the few scarce HBH
option codes still available. And, once locked in at whatever MTU field size we agree
on it will be impossible to change in the future. It is not complicated to make the field
sizes 32bits now, which would match RFCs 2675 and 4443.

Fred

From: ipv6 [mailto:ipv6-bounces@xxxxxxxx]
On Behalf Of touch@xxxxxxxxxxxxxx

Sent: Thursday, February 03, 2022 1:47 PM

To: last-call@xxxxxxxx

Cc: draft-ietf-6man-mtu-option@xxxxxxxx; ipv6@xxxxxxxx; IETF-Announce <ietf-announce@xxxxxxxx>; 6man-chairs@xxxxxxxx

Subject: [EXTERNAL] Re: [Last-Call] Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC

Why stop at 32 bits? They COULD expand to 128. Or 1024. Or more.

Right now, anything above 1500 is a unicorn outside closed environments (e.g., data centers):

https://tma.ifip.org/2018/wp-content/uploads/sites/3/2018/06/tma2018_paper57.pdf

A lot of the point of this option is to figure out what number below 1500 works - and/or when numbers even below those required for IPv6 minimums are needed.

If and when we ever get close to 64K, we could easily declare all 1’s as indicating the need for an extended value.

IMO, let’s not complicate things unnecessarily now.

Joe

—

Joe Touch, temporal epistemologist

www.strayalpha.com

On Feb 3, 2022, at 1:16 PM, Templin (US), Fred L <Fred.L.Templin@xxxxxxxxxx> wrote:

I have a comment - section 5 ("IPv6 Minimum Path MTU Hop-by-Hop Option") sets

aside two 16-bit fields to record MTU values. This places an upper bound  limit of

(2**16 - 1) octets on the MTU that can be recorded at each hop, but this will be

too small for IP parcels which can grow to (64 * (2**16 -1)) octets. And, if support

for true jumbos may be needed in the future the fields should probably permit sizes

up to (2**32 -1) octets which would require 32-bit fields.

Fred

-----Original Message-----

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Sent: Thursday, January 27, 2022 4:38 PM

To: IETF-Announce <ietf-announce@xxxxxxxx>

Cc: draft-ietf-6man-mtu-option@xxxxxxxx;
ipv6@xxxxxxxx; 
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Subject: Last Call: <draft-ietf-6man-mtu-option-12.txt> (IPv6 Minimum Path MTU Hop-by-Hop Option) to Experimental RFC

EXT email: be mindful of links/attachments.

The IESG has received a request from the IPv6 Maintenance WG (6man) to

consider the following document: - 'IPv6 Minimum Path MTU Hop-by-Hop Option'

 <draft-ietf-6man-mtu-option-12.txt> as Experimental RFC

The IESG plans to make a decision in the next few weeks, and solicits final

comments on this action. Please send substantive comments to the

last-call@xxxxxxxx mailing lists by 2022-02-10. Exceptionally, comments may

be sent to iesg@xxxxxxxx instead. In either case, please retain the beginning

of the Subject line to allow automated sorting.

Abstract

  This document specifies a new IPv6 Hop-by-Hop option that is used to

  record the minimum Path MTU along the forward path between a source

  host to a destination host.  The recorded value can then be

  communicated back to the source using the return Path MTU field in

  the option.

The file can be obtained via

https://datatracker.ietf.org/doc/draft-ietf-6man-mtu-option/

The following IPR Declarations may be related to this I-D:

  https://datatracker.ietf.org/ipr/4567/

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