Date: Thu, 13 Jan 2005 07:30:18 -0800 From: "Kevin Oberman" <oberman@es.net> To: Marian Durkovic <md@bts.sk> Cc: freebsd-net@freebsd.org Subject: Re: IPv6 TCP transfers are hanging Message-ID: <20050113153018.D2B4B5D07@ptavv.es.net> In-Reply-To: Your message of "Thu, 13 Jan 2005 07:51:16 %2B0100." <20050113065116.GA19940@us.svf.stuba.sk>
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> Date: Thu, 13 Jan 2005 07:51:16 +0100 > From: Marian Durkovic <md@bts.sk> > > Hi, > > > 08:20:12.680313 aaa.es.net.ssh > bbb.es.net.54854: . 10145:11573(1428) > > ack 31040 win 58548 <nop,nop,timestamp 9068204 69095244> [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
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