From owner-freebsd-net@FreeBSD.ORG Tue Jan 11 22:01:30 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 20BA116A4CE for ; Tue, 11 Jan 2005 22:01:30 +0000 (GMT) Received: from postal3.es.net (postal3.es.net [198.128.3.207]) by mx1.FreeBSD.org (Postfix) with ESMTP id C855143D1D for ; Tue, 11 Jan 2005 22:01:29 +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; Tue, 11 Jan 2005 14:01:29 -0800 Received: from ptavv (localhost [127.0.0.1]) by ptavv.es.net (Tachyon Server) with ESMTP id 356815D07; Tue, 11 Jan 2005 14:01:29 -0800 (PST) To: freebsd-net@freebsd.org Date: Tue, 11 Jan 2005 14:01:29 -0800 From: "Kevin Oberman" Message-Id: <20050111220129.356815D07@ptavv.es.net> cc: nesg@es.net Subject: 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: Tue, 11 Jan 2005 22:01:30 -0000 I think I have found a problem with TCP when run over IPv6. I set my MSS for TCP to 1460 to allow a full 1500 byte MTU to be utilized on my systems. (Yes, I see that this does break some things like communicating via links where PMTUD is blocked and one or more links restrict MTU to some size less than 1500 bytes. What I am specifically seeing is a packet being sent out with a TCP length of 1460. While this is fine for IPv4, it's too back for IPv6 and, as you might expect, the far end never receives this packet. There is a sysctl for net.inet.tcp.v6mssdflt which is set to 1024. This should be fine, but it appears that it is not being honored and the V4 value is always used. Am I mis-analyzing things or is TCP at least a bit broken when running over V6? (Or am I at fault for setting the large MSS because ti is honored with v6 even though there is a separate sysctl for IPv6? -- 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