From owner-freebsd-net@FreeBSD.ORG Sun Apr 29 16:21:25 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 B632A106566C for ; Sun, 29 Apr 2012 16:21:25 +0000 (UTC) (envelope-from lev@FreeBSD.org) Received: from onlyone.friendlyhosting.spb.ru (onlyone.friendlyhosting.spb.ru [46.4.40.135]) by mx1.freebsd.org (Postfix) with ESMTP id 75DF48FC19 for ; Sun, 29 Apr 2012 16:21:25 +0000 (UTC) Received: from lion.home.serebryakov.spb.ru (89.112.15.178.pppoe.eltel.net [89.112.15.178]) (Authenticated sender: lev@serebryakov.spb.ru) by onlyone.friendlyhosting.spb.ru (Postfix) with ESMTPA id B3BC14AC2D for ; Sun, 29 Apr 2012 20:21:24 +0400 (MSK) Date: Sun, 29 Apr 2012 20:21:23 +0400 From: Lev Serebryakov Organization: FreeBSD X-Priority: 3 (Normal) Message-ID: <1683134664.20120429202123@serebryakov.spb.ru> To: freebsd-net@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: IPv6 tunnel MTU problems: it seems to be gif problem X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: lev@FreeBSD.org List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 29 Apr 2012 16:21:25 -0000 Hello, Freebsd-net. man gif says: If the outer protocol is IPv4, gif does not try to perform path MTU dis- covery for the encapsulated packet (DF bit is set to 0). If the outer protocol is IPv6, path MTU discovery for encapsulated pack- ets may affect communication over the interface. The first bigger-than- pmtu packet may be lost. To avoid the problem, you may want to set the interface MTU for gif to 1240 or smaller, when the outer header is IPv6 and the inner header is IPv4. So, it seems, when "outer" interface has MTU less than 1500 (1460, for example, as in my case), MTU on gif interface should be set less (even if outer protocol is IPv4, and inner one is IPv6). But gif doesn't allow MTU less than default 1280 (if_gif.h contains this constant)... Could it be source with my problems with IPv6-over-IPv4-over-PPPoE tunnel? Should sources of if_gif be fixed? Or man page? -- // Black Lion AKA Lev Serebryakov