On Fri, 4 Feb 2022, 10:38 Tom Herbert, <tom@xxxxxxxxxxxxxxx> wrote:
On Thu, Feb 3, 2022 at 3:16 PM touch@xxxxxxxxxxxxxx
<touch@xxxxxxxxxxxxxx> wrote:
>
> Fair enough. Two more bytes burned for largely no reason for the foreseeable future, but so be it.
Joe,
It's more like eight more bytes burned since both two byte fields need
to be extended to four bytes and the EH needs to be padded to have
length in units of eight bytes. Given that MTU's that exceed 64K are
exceedingly rare, this does seem like a lot of overhead to add to
potentially every packet. Also, if the sender already knows that its
local MTU is less than 64K, the discovery that the network supports a
higher MTU doesn't seem to be useful information. An alternative might
be to define a long format of the option with larger MTU fields that
can coexist with the already defined option. This could be done by
using the same option type number, but discriminating between to the
two formats based on the option length.
Or perhaps another spec to describe how the IPv6 Jumbogram EH works in combination with this.
Regards,
Mark.
Tom
> —
> Joe Touch, temporal epistemologist
> www.strayalpha.com
>
> On Feb 3, 2022, at 2:13 PM, Templin (US), Fred L <Fred.L.Templin@xxxxxxxxxx> wrote:
>
> 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-----
> From: ipv6 [mailto:ipv6-bounces@xxxxxxxx] On Behalf Of The IESG
> Sent: Thursday, January 27, 2022 4:38 PM
> To: IETF-Announce <ietf-announce@xxxxxxxx>
> Cc: draft-ietf-6man-mtu-option@xxxxxxxx; ipv6@xxxxxxxx; 6man-chairs@xxxxxxxx
> 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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