Date: Fri, 15 May 2009 00:09:02 +0200 (CEST) From: sthaug@nethelp.no To: oberman@es.net Cc: freebsd-net@freebsd.org Subject: Re: IPv6 fragmentation weirdness Message-ID: <20090515.000902.74658525.sthaug@nethelp.no> In-Reply-To: <20090514214235.B09701CC12@ptavv.es.net> References: <20090514214235.B09701CC12@ptavv.es.net>
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> First, why is the kernel fragmenting this at all as it fits in the > interface MTU? Good question, I definitely disagree with this behavior and would say that it breaks POLA. But it's documented (see the ping6 -m option). > Can anyone fetch anything from ftp.funet.fi via IPv6? I suspect it is > something in the path that is blocking my traffic, so others may not see > this, but I think the root issues is the kernel fragmenting packets way > below MTU size. I just picked up a copy of the 7.2 bootonly ISO image using IPv6. Slow but usable. My path (from Oslo, Norway) is: sthaug@lab1% traceroute6 ftp.funet.fi traceroute6 to ftp.funet.fi (2001:708:10:9::20:1) from 2001:8c0:8b00:1::2, 64 hops max, 12 byte packets 1 ge-0-0-9-515.br1.fn3.no.catchbone.net 0.254 ms 4.917 ms 0.203 ms 2 c10G-ge-5-1-0.cr2.osls.no.catchbone.net 0.485 ms 0.408 ms 0.399 ms 3 c10G-xe-4-1-0.br1.osls.no.catchbone.net 0.364 ms 0.351 ms 0.361 ms 4 2001:2000:3083:6::1 9.006 ms 8.848 ms 8.966 ms 5 s-ipv6-b1-link.ipv6.telia.net 19.481 ms 19.590 ms 19.412 ms 6 2001:2000:3080:d::2 110.907 ms 109.056 ms 119.495 ms 7 helsinki0-rtr.funet.fi 116.305 ms 123.534 ms 119.472 ms 8 csc0-x0000-helsinki0.ipv6.funet.fi 118.873 ms 117.439 ms 116.054 ms 9 ftp.funet.fi 115.777 ms 116.087 ms 117.735 ms Note that the IPv6 transit from Telia is tunnelled, and the RTT is awful compared to IPv4 (IPv4 RTT to ftp.funet.fi from the same box is around 17 ms). Steinar Haug, Nethelp consulting, sthaug@nethelp.no
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