From owner-freebsd-net@FreeBSD.ORG Sat Dec 26 21:56:22 2009 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 C5664106568D for ; Sat, 26 Dec 2009 21:56:22 +0000 (UTC) (envelope-from hyama99@gmail.com) Received: from ey-out-2122.google.com (ey-out-2122.google.com [74.125.78.27]) by mx1.freebsd.org (Postfix) with ESMTP id 6BD3B8FC16 for ; Sat, 26 Dec 2009 21:56:22 +0000 (UTC) Received: by ey-out-2122.google.com with SMTP id 9so1134395eyd.3 for ; Sat, 26 Dec 2009 13:56:21 -0800 (PST) MIME-Version: 1.0 Received: by 10.216.89.18 with SMTP id b18mr4737098wef.14.1261863208046; Sat, 26 Dec 2009 13:33:28 -0800 (PST) Date: Sun, 27 Dec 2009 06:33:28 +0900 Message-ID: <90dbee150912261333l602c4161nccaf1995dc83699a@mail.gmail.com> From: Hideki Yamamoto To: freebsd-net@freebsd.org Content-Type: text/plain; charset=ISO-8859-1 Subject: GIF MTU parmeter is needed 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: Sat, 26 Dec 2009 21:56:22 -0000 Hi, I often use FreeBSD for developing the gateway. For example, I use gif for the tunnel protocol when using IPv6 over IPv4 and use an application for changing packet address for special purpose. When we were using old FreeBSD, such as FreeBSD 4.11, the MTU of the tunnel packets or forwarded packets was not limited into 1280. However, FreeBSD 6,7, and 8 fragments packets by 1280 when using tunnel. I know that this behavior is based on the RFC specification. However it is not useful when using AV application that use around 1400B RTP packet. AV packets will be fragmented into long packets (1280) and short packets (1400-1280) when using tunnel, and short packet will sometimes be lost by network. I hope new parameter by sysctl to control MTU of tunnel will be implemented. The following is an example of new paramter to control MTU size. net.inet6.use_mmtu :1 --- is the same as current versions, it means minimum MTU 1280 will be used when gateway node. :0--- is the same as the old versions. It means OS uses as long MTU size as possible ( I hope "1" will be default) Are there any comment on this matter? Best regards, Hideki Yamamoto