Re: Minimum IPv6 MTU

Jeroen Massar <> Thu, 10 July 2008 21:34 UTC

Return-Path: <>
Received: from [] (localhost []) by (Postfix) with ESMTP id 47AEF3A6A9E; Thu, 10 Jul 2008 14:34:37 -0700 (PDT)
Received: from localhost (localhost []) by (Postfix) with ESMTP id 758FB3A6A9E for <>; Thu, 10 Jul 2008 14:34:36 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.523
X-Spam-Status: No, score=-1.523 tagged_above=-999 required=5 tests=[AWL=-1.077, BAYES_00=-2.599, FRT_BELOW2=2.154, NO_RELAYS=-0.001]
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id CFIKADGpWRBG for <>; Thu, 10 Jul 2008 14:34:35 -0700 (PDT)
Received: from ( [IPv6:2001:41e0:ff00:0:216:3eff:fe00:4]) by (Postfix) with ESMTP id AE4333A6A8F for <>; Thu, 10 Jul 2008 14:34:34 -0700 (PDT)
Received: from [IPv6:2001:41e0:ff42:b00:216:cfff:fe00:e7d0] ( [IPv6:2001:41e0:ff42:b00:216:cfff:fe00:e7d0]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: jeroen) by (Postfix) with ESMTPSA id 1396F35A539; Thu, 10 Jul 2008 23:34:46 +0200 (CEST)
Message-ID: <>
Date: Thu, 10 Jul 2008 23:34:44 +0200
From: Jeroen Massar <>
Organization: Unfix
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20080421 Lightning/0.8 Thunderbird/ Mnenhy/
MIME-Version: 1.0
To: Fernando Gont <>
Subject: Re: Minimum IPv6 MTU
References: <>
In-Reply-To: <>
X-Enigmail-Version: 0.95.6
OpenPGP: id=333E7C23
X-Virus-Scanned: ClamAV version 0.93.1, clamav-milter version 0.93.1 on
X-Virus-Status: Clean
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
Content-Type: multipart/mixed; boundary="===============0437129824=="

Fernando Gont wrote:
> Folks,
> RFC 2460 states that every link in an internet have an MTU of 1280 
> octets or greater, and that any link that cannot convey a 1280-octet 
> packet in one piece must provide fragmentation and reassembly at a layer 
> bellow IPv6.
> However, while talking about the specs with a few folks (who preferred 
> to remain anonymous), it was mentioned to me that in a number of 
> scenarios (not necessarily those that involve tunnels), some links have 
> an MTU smaller than 1280, and they do not perform the "fragmentation and 
> reassembly function at a layer bellow IP" that RFC 2460 requires.

Then those links have to be fixed. Simple, nothing to it ;)

This is why there are a couple of RFC's that explicitly detail how these 
links are used to transmit/use IPv6. Some for instance don't support 
multicast which thus breaks the whole concept of Neighbor Discovery etc.

Thus if you know any linktype which is not able yet to properly do IPv6, 
document them as a draft and submit it.


IETF IPv6 working group mailing list
Administrative Requests: