Re: [v4tov6transition] [Softwires] 6a44 MTU issues

"Templin, Fred L" <Fred.L.Templin@boeing.com> Wed, 13 October 2010 15:16 UTC

Return-Path: <Fred.L.Templin@boeing.com>
X-Original-To: v4tov6transition@core3.amsl.com
Delivered-To: v4tov6transition@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 673F43A6B1C; Wed, 13 Oct 2010 08:16:22 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.051
X-Spam-Level:
X-Spam-Status: No, score=-6.051 tagged_above=-999 required=5 tests=[AWL=0.248, BAYES_00=-2.599, MIME_8BIT_HEADER=0.3, RCVD_IN_DNSWL_MED=-4]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xm89teGlTFPn; Wed, 13 Oct 2010 08:16:20 -0700 (PDT)
Received: from stl-smtpout-01.boeing.com (stl-smtpout-01.boeing.com [130.76.96.56]) by core3.amsl.com (Postfix) with ESMTP id 620DE3A696F; Wed, 13 Oct 2010 08:16:20 -0700 (PDT)
Received: from blv-av-01.boeing.com (blv-av-01.boeing.com [130.247.48.231]) by stl-smtpout-01.ns.cs.boeing.com (8.14.4/8.14.4/8.14.4/SMTPOUT) with ESMTP id o9DFHYff020420 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL); Wed, 13 Oct 2010 10:17:34 -0500 (CDT)
Received: from blv-av-01.boeing.com (localhost [127.0.0.1]) by blv-av-01.boeing.com (8.14.4/8.14.4/DOWNSTREAM_RELAY) with ESMTP id o9DFHXiT027311; Wed, 13 Oct 2010 08:17:33 -0700 (PDT)
Received: from XCH-NWHT-04.nw.nos.boeing.com (xch-nwht-04.nw.nos.boeing.com [130.247.64.250]) by blv-av-01.boeing.com (8.14.4/8.14.4/UPSTREAM_RELAY) with ESMTP id o9DFHX9f027305 (version=TLSv1/SSLv3 cipher=RC4-MD5 bits=128 verify=OK); Wed, 13 Oct 2010 08:17:33 -0700 (PDT)
Received: from XCH-NW-01V.nw.nos.boeing.com ([130.247.64.97]) by XCH-NWHT-04.nw.nos.boeing.com ([130.247.64.250]) with mapi; Wed, 13 Oct 2010 08:17:33 -0700
From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: =?iso-8859-1?Q?R=E9mi_Despr=E9s?= <remi.despres@free.fr>, Washam Fan <washam.fan@gmail.com>
Date: Wed, 13 Oct 2010 08:17:32 -0700
Thread-Topic: [Softwires] [v4tov6transition] 6a44 MTU issues
Thread-Index: Actp3rJNfhayY60TRWKuORiNpJ58hgBCW2ow
Message-ID: <E1829B60731D1740BB7A0626B4FAF0A65C59BDE54A@XCH-NW-01V.nw.nos.boeing.com>
References: <C8D29306.3EDBD%yiu_lee@cable.comcast.com><E1829B60731D1740BB7A0 626B4FAF0A65C59B79387@XCH-NW-01V.nw.nos.boeing.com><E1829B60731D1740BB7A062 6B4FAF0A65C59B79491@XCH-NW-01V.nw.nos.boeing.com><AANLkTik0_9CRSfi_O53MChgt 5QH+-=aR8HO7v+fHiLwY@mail.gmail.com><D8BB9123-C611-4476-AFA1-D0ADEEDB6270@f ree.fr><E1829B60731D1740BB7A0626B4FAF0A65C59B797F3@XCH-NW-01V.nw.nos.boeing .com><279A3292-A291-4BC0-8FCF-53120066931E@free.fr><E1829B60731D1740BB7A062 6B4FAF0A65C59B7982A@XCH-NW-01V.nw.nos.boeing.com><E1829B60731D1740BB7A0626B4FAF0A65C59B79898@XCH-NW-01V.nw.nos.boeing.com> <0DD3B2BD-0200-4CC9-A78F-9AB9F574FA3A@free.fr>
In-Reply-To: <0DD3B2BD-0200-4CC9-A78F-9AB9F574FA3A@free.fr>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
acceptlanguage: en-US
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Cc: Softwires <softwires@ietf.org>, "v4tov6transition@ietf.org" <v4tov6transition@ietf.org>
Subject: Re: [v4tov6transition] [Softwires] 6a44 MTU issues
X-BeenThere: v4tov6transition@ietf.org
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: <v4tov6transition.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/listinfo/v4tov6transition>, <mailto:v4tov6transition-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/v4tov6transition>
List-Post: <mailto:v4tov6transition@ietf.org>
List-Help: <mailto:v4tov6transition-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/v4tov6transition>, <mailto:v4tov6transition-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 13 Oct 2010 15:16:22 -0000

Hi Remi, 

> -----Original Message-----
> From: softwires-bounces@ietf.org 
> [mailto:softwires-bounces@ietf.org] On Behalf Of Rémi Després
> Sent: Tuesday, October 12, 2010 12:26 AM
> To: Templin, Fred L; Washam Fan
> Cc: Softwires; v4tov6transition@ietf.org
> Subject: Re: [Softwires] [v4tov6transition] 6a44 MTU issues
> 
> Fred and Washam,
> 
> I reacted too fast to previous remarks when I proposed to 
> modify the accepted IPv6 MTU in 6a44 draft.
> If IPv6 packets longer than 1280 would be accepted by 6a44 
> servers, hosts could receive them in fragmented IPv4 datagrams.

Or they might be reassembled in the NAT(s) in front of
the host.

> This would be contrary to the objective of simplicity 
> (datagram reassembly would have to be include in 6a44 
> clients) and to the objective of security (a new door would 
> be open to dos attacks).
> No change on this point will therefore appear in the next 
> version of the draft. 
> Some additional explanations may be appropriate, but 
> preferably after a consensus on what has to be said.
> 
> Then the MTU issue of IPv6 in IPv6 tunnels that Fred 
> underlines remains as is.

Right.

> If the PMTU of such a tunnel is unknown, or known to be less 
> than 1280+40,

Actually, 1280+40+IPsec headers and trailers in the case
of VPN.

> tunnel endpoints have to tunnel 1280-octets 
> external packets in two pieces, using a fragmented IPv6 
> datagram for this.

OK, so steady-state IPv6 fragmentation and reassembly between
VPN tunnel endpoints is expected as normal operation in this
model.

> Reassembly at the other end is then necessary. 
> It can be facilitated if the tunnel is treated as only one 
> flow,

Can you say more about what you mean by this?

> with packets in general kept in sequential order.

In-order delivery is not a strict requirement for
correct IPv6 reassembly - but the fact that steady-state
IPv6 frag/reass is required seems onerous.

Fred
fred.l.templin@boeing.com

> Regards,
> RD
>   
> 
> >>>> Actually, the 6a44 specification should, instead of 1280, 
> >>>> require IPv4 MTU - 28 octets, both for hairpinning and 
> >>>> traversal cases.
> >>> 
> >>> How can you be sure that IPv4 PMTUD will work in
> >>> the traversal case?
> >> 
> >> In the to-host direction, because the ISP network is all what 
> >> is left to traverse before reaching the CPE.
> > 
> > In what you call the to-host direction, any ICMPv4
> > returned from the ISP network might not have enough
> > information for stateless translation to ICMPv6.
> 
> 1. Could you be more specific?
> Do yout see a significant difference with what happens with 6to4,
> 
> 
> >> In the from host direction, one can't be sure, but doesnt' need to.
> >> If a smaller PMTU is encountered further downstream, a PTB 
> >> ICMPv6 error message will be returned from there.
> > 
> > In the from-host direction, any ICMPv4 returned from
> > the ISP network might not be delivered to the tunnel
> > endpoint due to NAT filtering,
> 
> 2. Then the IPv6 service is somewhat damaged concerning fault 
> diagnosing, like the underlying IPv4 service.
> But at least packets that should be delivered are delivered.
> 
> 
> > and might not have
> > enough information for stateless translation to ICMPv6.
> 
> 3. Same as 1. above.
> 
> 
> >>> In the to-host direction, because the ISP network is all what 
> >>> is left to traverse before reaching the CPE.
> >> 
> >> In what you call the to-host direction, any ICMPv4
> >> returned from the ISP network might not have enough
> >> information for stateless translation to ICMPv6.
> > 
> > I should also say, any ICMPv4 returned from within
> > the end user network (where MTUs might not be so well
> > managed) might not be delivered to the tunnel endpoint
> > in the ISP network.
> 
> 4. Same as 2. above.
> (Since IPv4 fragments rather than returning packet-too-big 
> ICMP messages, this cannot concern MTUs).
> 
> Yet, there remains another problem with the replacement of 
> 1280 by "IPv4 MTU - 28" (I proposed it too quickly) because 
> it creates risks of fragmentation ...
>   
> 
> 
> 
> 
> 
> _______________________________________________
> Softwires mailing list
> Softwires@ietf.org
> https://www.ietf.org/mailman/listinfo/softwires
>