From owner-freebsd-net@FreeBSD.ORG Wed Jan 4 12:01:18 2012 Return-Path: Delivered-To: freebsd-net@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 54AEC1065670 for ; Wed, 4 Jan 2012 12:01:18 +0000 (UTC) (envelope-from hrs@FreeBSD.org) Received: from mail.allbsd.org (gatekeeper-int.allbsd.org [IPv6:2001:2f0:104:e002::2]) by mx1.freebsd.org (Postfix) with ESMTP id 9C2288FC1C for ; Wed, 4 Jan 2012 12:01:17 +0000 (UTC) Received: from alph.allbsd.org ([IPv6:2001:2f0:104:e010:862b:2bff:febc:8956]) (authenticated bits=128) by mail.allbsd.org (8.14.4/8.14.4) with ESMTP id q04C14ZC094814; Wed, 4 Jan 2012 21:01:14 +0900 (JST) (envelope-from hrs@FreeBSD.org) Received: from localhost (localhost [IPv6:::1]) (authenticated bits=0) by alph.allbsd.org (8.14.4/8.14.4) with ESMTP id q04C12td023663; Wed, 4 Jan 2012 21:01:04 +0900 (JST) (envelope-from hrs@FreeBSD.org) Date: Wed, 04 Jan 2012 20:59:31 +0900 (JST) Message-Id: <20120104.205931.1091341202993271005.hrs@allbsd.org> To: sodynet1@gmail.com From: Hiroki Sato In-Reply-To: References: X-PGPkey-fingerprint: BDB3 443F A5DD B3D0 A530 FFD7 4F2C D3D8 2793 CF2D X-Mailer: Mew version 6.3.51 on Emacs 23.3 / Mule 6.0 (HANACHIRUSATO) Mime-Version: 1.0 Content-Type: Multipart/Signed; protocol="application/pgp-signature"; micalg=pgp-sha1; boundary="--Security_Multipart(Wed_Jan__4_20_59_31_2012_820)--" Content-Transfer-Encoding: 7bit X-Virus-Scanned: clamav-milter 0.97 at gatekeeper.allbsd.org X-Virus-Status: Clean X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (mail.allbsd.org [IPv6:2001:2f0:104:e001::32]); Wed, 04 Jan 2012 21:01:15 +0900 (JST) X-Spam-Status: No, score=-104.6 required=13.0 tests=BAYES_00, CONTENT_TYPE_PRESENT, RDNS_NONE, SPF_SOFTFAIL, USER_IN_WHITELIST autolearn=no version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on gatekeeper.allbsd.org Cc: freebsd-net@FreeBSD.org Subject: Re: kernel: nd6_setmtu0: new link MTU on ng29 (1218) is too small for IPv6 X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 04 Jan 2012 12:01:18 -0000 ----Security_Multipart(Wed_Jan__4_20_59_31_2012_820)-- Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sami Halabi wrote in : so> Hi, so> I'm using a FreeBSD8.2-R-p5 in conjunction with MPD5.5 port for creating so> pptp/l2tp tunnels. so> so> I'm using MPPC (Compression & Encryption), my current onfiguration i use so> only IPv4. so> so> I keep getting in the logs the following: so> Jan 3 19:15:21 mpd2 kernel: nd6_setmtu0: new link MTU on ng120 (1218) is so> too small for IPv6 so> Jan 3 20:00:40 mpd2 kernel: nd6_setmtu0: new link MTU on ng151 (1218) is so> too small for IPv6 so> Jan 3 20:09:27 mpd2 kernel: nd6_setmtu0: new link MTU on ng128 (1218) is so> too small for IPv6 so> Jan 3 20:30:13 mpd2 kernel: nd6_setmtu0: new link MTU on ng128 (1218) is so> too small for IPv6 so> Jan 3 20:34:33 mpd2 kernel: nd6_setmtu0: new link MTU on ng137 (1218) is so> too small for IPv6 so> Jan 3 21:06:46 mpd2 kernel: nd6_setmtu0: new link MTU on ng105 (1218) is so> too small for IPv6 so> Jan 3 21:42:48 mpd2 kernel: nd6_setmtu0: new link MTU on ng92 (1218) is so> too small for IPv6 so> Jan 3 22:12:49 mpd2 kernel: nd6_setmtu0: new link MTU on ng137 (1218) is so> too small for IPv6 so> Jan 3 23:21:50 mpd2 kernel: nd6_setmtu0: new link MTU on ng92 (1218) is so> too small for IPv6 so> Jan 4 00:00:36 mpd2 kernel: nd6_setmtu0: new link MTU on ng105 (1218) is so> too small for IPv6 so> Jan 4 00:34:48 mpd2 kernel: nd6_setmtu0: new link MTU on ng105 (1218) is so> too small for IPv6 so> Jan 4 07:47:37 mpd2 kernel: nd6_setmtu0: new link MTU on ng100 (1218) is so> too small for IPv6 so> Jan 4 08:31:55 mpd2 kernel: nd6_setmtu0: new link MTU on ng116 (1218) is so> too small for IPv6 so> Jan 4 09:16:21 mpd2 kernel: nd6_setmtu0: new link MTU on ng123 (1218) is so> too small for IPv6 so> Jan 4 12:55:32 mpd2 kernel: nd6_setmtu0: new link MTU on ng53 (1218) is so> too small for IPv6 so> so> although the NG tunnels don't negotiate IPv6. so> so> a close look to the MPD log i see that this happens for connections that so> set MRU/MTU 1400. so> so> I talked to MPD developer (Alexander Motin) and this isn't a MPD problem, so> rather than a kernel issue as the logs say. so> so> why this problem happens when no IPv6 is in work? so> so> I don't want to disable ipv6 completely since i have plans in using it in so> the near future. It is because the end point of an L2TPv2 tunnel is implemented in MPD by using ng_iface(4), and it always has an inet6 hook when the kernel has IPv6 support (note that GENERIC kernel supports IPv6). This means an ngNNN interface is always IPv6-capable regardless of whether the tunnel supports IPv6 as the inner protocol (typically via IPV6CP in the case of L2TPv2) or not. IPv6 communication is denied when the tunnel does not support IPv6, but the interface ngNNN itself always supports IPv6. Thus, the warning you got is caused by a side-effect of IPv6 initialization of ngNNN. Since IPv6 specification requires the minimum MTU as 1280, an warning message will be displayed if you try to use a smaller MTU as the link MTU than that. You can ignore the messages safely, or increasing the MTU will suppress them. I am still wondering why the message appears when MTU is set to 1400, however. In the case of L2TPv2 over UDPv4, MTU reduction should be 46 because of encapsulation by IPv4, UDP, L2TP, and PPP. -- Hiroki ----Security_Multipart(Wed_Jan__4_20_59_31_2012_820)-- Content-Type: application/pgp-signature Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEABECAAYFAk8EPyMACgkQTyzT2CeTzy19EQCfV4dvFE6cRx2RjkTjTUBxlPnl 9K8AoJHdSdbDWaynjpo3CEj+S3SC2R/c =kt/G -----END PGP SIGNATURE----- ----Security_Multipart(Wed_Jan__4_20_59_31_2012_820)----