From owner-freebsd-net@FreeBSD.ORG Thu Jan 13 15:30:19 2005 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id BA9AC16A4D1 for ; Thu, 13 Jan 2005 15:30:19 +0000 (GMT) Received: from postal3.es.net (postal3.es.net [198.128.3.207]) by mx1.FreeBSD.org (Postfix) with ESMTP id 728AC43D54 for ; Thu, 13 Jan 2005 15:30:19 +0000 (GMT) (envelope-from oberman@es.net) Received: from ptavv.es.net ([198.128.4.29]) by postal3.es.net (Postal Node 3) with ESMTP (SSL) id IBA74465; Thu, 13 Jan 2005 07:30:19 -0800 Received: from ptavv (localhost [127.0.0.1]) by ptavv.es.net (Tachyon Server) with ESMTP id D2B4B5D07; Thu, 13 Jan 2005 07:30:18 -0800 (PST) To: Marian Durkovic In-reply-to: Your message of "Thu, 13 Jan 2005 07:51:16 +0100." <20050113065116.GA19940@us.svf.stuba.sk> Date: Thu, 13 Jan 2005 07:30:18 -0800 From: "Kevin Oberman" Message-Id: <20050113153018.D2B4B5D07@ptavv.es.net> cc: freebsd-net@freebsd.org Subject: Re: IPv6 TCP transfers are hanging X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 13 Jan 2005 15:30:19 -0000 > Date: Thu, 13 Jan 2005 07:51:16 +0100 > From: Marian Durkovic > > Hi, > > > 08:20:12.680313 aaa.es.net.ssh > bbb.es.net.54854: . 10145:11573(1428) > > ack 31040 win 58548 [flowlabel 0x6ae53] > > len 1460, hlim 64) > > 1428 bytes is the proper payload length for TCPv6 with options > 1448 bytes is the same for TCPv4 > > 1440 bytes is the payload length for TCPv6 without options > 1460 byts is the same for TCPv4 > > If such packets are failing, your path MTU is probably not 1500 bytes but > smaller. Indeed, that is the case. One link is via a GRE tunnel and that is restricting MTU. What I don't understand is how this is happening. tcp.mssdflt is set to 1400 bytes and tcp.v6mssdflt is only 1024. If PMTU discovery was working, this should not be a problem. If PMTU discovery is not used, the MSS defaults should keep the packets small enough to work over the tunnel. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634