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Re: [v6ops] LAN vs WAN MTUs (was new draft: draft-byrne-v6ops-64share)

Rémi Després <despres.remi@laposte.net> Mon, 01 October 2012 13:34 UTC

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From: Rémi Després <despres.remi@laposte.net>
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Date: Mon, 01 Oct 2012 15:34:29 +0200
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References: <201209291245.q8TCj0P22972@ftpeng-update.cisco.com> <alpine.DEB.2.00.1209291932550.13902@uplift.swm.pp.se> <CAD6AjGT_V05m8fU-cUfFKhPHvyrgiJihQoS_bF-j-w3XLgBEcQ@mail.gmail.com> <97EB7536A2B2C549846804BBF3FD47E11184A36D@xmb-aln-x02.cisco.com> <CAD6AjGRNHHqrj8R7-gkMAsC11B+AQOoZOV4jH4kTHXBFcDBsiA@mail.gmail.com> <20121001000808.GB25686@srv03.cluenet.de> <CAKD1Yr2ds8tZTou-pZ+oQJ8yeOt5g432s7h5LsFoFs9iz5_K8Q@mail.gmail.com> <20121001095516.GA9562@srv03.cluenet.de> <alpine.DEB.2.00.1210011219350.13902@uplift.swm.pp.se>
To: Daniel Roesen <dr@cluenet.de>, Mikael Abrahamsson <swmike@swm.pp.se>
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Cc: v6ops WG <v6ops@ietf.org>
Subject: Re: [v6ops] LAN vs WAN MTUs (was new draft: draft-byrne-v6ops-64share)
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Hi, Daniel, Mikael, 

2012-10-01 12:26, Mikael Abrahamsson :

> On Mon, 1 Oct 2012, Daniel Roesen wrote:
> ...
>> If you really care about delay, MSS clamping is an option which isn't intrusive to the LAN as it affects only connections via the mobile gateway.
> 
> But it only helps TCP, not everything else.

Since it does help TCP and doesn't hurt anything, it's IMHO worth recommending.

FYI, something was proposed about this in May, ref. www.ietf.org/mail-archive/web/v6ops/current/msg13015.html, namely:
"In any node, before entering of just after leaving a link whose MTU is the same in both directions (Ethernet, 6rd, DS-lite, ...), if the MSS advertised in a received TCP SYN packet exceeds the link MTU minus the TCP/IP header length (40 octets in IPv4, 60 in IPv6), reduce it to this value, and adjust IP and TCP checksums accordingly."

In principle, I can't any longer afford to be active in v6ops, but still look at some of the exchanged mails and may provide brief comments. Dan Wing is added as cc because he privately said in May he liked this proposed behavior.

Regards,
RD

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