From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02858C35254 for ; Wed, 5 Feb 2020 12:28:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6819217BA for ; Wed, 5 Feb 2020 12:28:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727963AbgBEM2Q (ORCPT ); Wed, 5 Feb 2020 07:28:16 -0500 Received: from relay.cooperix.net ([176.58.120.209]:49756 "EHLO relay.sandelman.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727892AbgBEM2P (ORCPT ); Wed, 5 Feb 2020 07:28:15 -0500 X-Greylist: delayed 393 seconds by postgrey-1.27 at vger.kernel.org; Wed, 05 Feb 2020 07:28:14 EST Received: from dooku.sandelman.ca (ip5f5bd76d.dynamic.kabel-deutschland.de [95.91.215.109]) by relay.sandelman.ca (Postfix) with ESMTPS id 4B8E61F45A; Wed, 5 Feb 2020 12:21:40 +0000 (UTC) Received: by dooku.sandelman.ca (Postfix, from userid 179) id 6A87F1314; Wed, 5 Feb 2020 07:21:37 -0500 (EST) From: Michael Richardson To: Alexander Aring cc: netdev@vger.kernel.org Subject: Re: [PATCH net 0/2] net: ipv6: seg6: headroom fixes In-reply-to: <20200204173019.4437-1-alex.aring@gmail.com> References: <20200204173019.4437-1-alex.aring@gmail.com> Comments: In-reply-to Alexander Aring message dated "Tue, 04 Feb 2020 12:30:17 -0500." X-Mailer: MH-E 8.6; nmh 1.6; GNU Emacs 25.1.1 MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Date: Wed, 05 Feb 2020 13:21:37 +0100 Message-ID: <26689.1580905297@dooku.sandelman.ca> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org --=-=-= Content-Type: text/plain Alexander Aring wrote: > This patch series fixes issues which I discovered while implementing RPL > source routing for 6LoWPAN interfaces. 6LoWPAN interfaces are using a MTU > of 1280 which is the IPv6 minimum MTU. I suppose this is the right fix to > do that according to my explanation that tunnels which acting before L3 > need to set this headroom. So far I see only segmentation route is affected > to it. Maybe BPF tunnels, but it depends on the case... Maybe a comment > need to be added there as well to not getting confused. If wanted I can > send another patch for a comment for net-next or even net? May the > variable should be renamed to l2_headroom? I had discussed this with Alex over the past few days. I had not looked closely at the code during that discussion, and maybe my comments in chat were wrong. So these patches don't look right to me. I think that the issue we have here is that things are big vague when it comes to layer-2.5's, and fatter layer-3s. Maybe this is well established in lore... My understanding is that headroom is a general offset, usually set by the L2 which tells the L3/L4 how much to offset in the SKB before the ULP header is inserted. TCP/UDP/SCTP/ESP need to know this. MPLS is a layer-2.5, and so it quite weird, because it creates a new L2 which lives upon other L2 and also other L3s. Segment routing, and RPL RH3 headers involve a fatter L3 header. Of course, one could mix all of these things together! -- ] Never tell me the odds! | ipv6 mesh networks [ ] Michael Richardson, Sandelman Software Works | network architect [ ] mcr@sandelman.ca http://www.sandelman.ca/ | ruby on rails [ --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEERK+9HEcJHTJ9UqTMlUzhVv38QpAFAl46s1AACgkQlUzhVv38 QpBXbAf/esJasXYzIXpM5QlQ86jcP9DTVkAbAR5aZ6ROozi9/IdiPq8k6naBIlSj zWfFfCFnt9B0fpidq4DFlNaBLtZGFCZS7CHWuXtjZO0keW4yttiuNEYrxfsirHPu HqNHihTN8gRFGjS6QhjqliRiJS0eaH63xvCVssqDzD7kNnmGtk/uTHxBexw5Z+nG j4LW7zzukVYSfM/hzjFsissC0G+4oiuCKRaHUEMisCSmwR+fftE+Z0ZPW+A1OFiu gS3lhTw7lD5SUkBUxNlT2E6CGen6hn48ToWw6Wzy/tGo27k1D9PBynh+XVDfx8CK utDTdAG6fKhWvBfMMPVCbJE2hugjcA== =/Oxf -----END PGP SIGNATURE----- --=-=-=--