Hi all, I'm facing a strange thing with IPv6 and IMCPv6 packet too big messages. I have an FTP server (running 5.0 tagged sources, PF disabled) accessible through IPv6 via a gif(4) tunnel on a gateway (running ftp-proxy(8) on a -current machine). On this gateway, the MTU of the gif(4) interface is 1280. On the FTP server and on the local gateway interface, the MTU is 1500.
When I start to download a file on a client behind the gateway, the FTP server begins to send the file with too large packets. The gateway then sends ICMPv6 packet too big: 00:17:04.169906 2001:470:dead:2::12.21 > 2001:470:dead:2::1.36810: P 548:4166408094(-128559750) ack 93 win 2142 <nop,nop,timestamp 3508338349 1153050903> [flowlabel 0x5bc2b] (len 110, hlim 64) 00:17:04.170489 2001:470:dead:2::12.50013 > 2001:470:dead:2::1.56555: . 1:4166409025(-128558272) ack 1 win 2130 [flowlabel 0x69a54] (len 1440, hlim 64) 00:17:04.170523 2001:470:dead:2::12.50013 > 2001:470:dead:2::1.56555: . 1421:4166410581(-128558136) ack 1 win 2130 [flowlabel 0x69a54] (len 1440, hlim 64) 00:17:04.170557 2001:470:dead:2::12.50013 > 2001:470:dead:2::1.56555: . 2841:4166412137(-128558000) ack 1 win 2130 [flowlabel 0x69a54] (len 1440, hlim 64) 00:17:04.170563 2001:470:dead:2::12.50013 > 2001:470:dead:2::1.56555: . 4261:4166413693(-128557864) ack 1 win 2130 [flowlabel 0x69a54] (len 1440, hlim 64) 00:17:04.171095 2001:470:dead:2::1 > 2001:470:dead:2::12: icmp6: too big 1280 (len 1240, hlim 64) 00:17:04.171506 2001:470:dead:2::1 > 2001:470:dead:2::12: icmp6: too big 1280 (len 1240, hlim 64) 00:17:04.171619 2001:470:dead:2::1 > 2001:470:dead:2::12: icmp6: too big 1280 (len 1240, hlim 64) 00:17:04.171735 2001:470:dead:2::1 > 2001:470:dead:2::12: icmp6: too big 1280 (len 1240, hlim 64) 00:17:04.360967 2001:470:dead:2::1.36810 > 2001:470:dead:2::12.21: . 93:4166408785(-128558604) ack 626 win 2048 <nop,nop,timestamp 1153050903 3508338349> [flowlabel 0x9f0e3] (len 32, hlim 64) Then, nothing happens, the download on the client side stalls. The FTP server doesn't try to retransmit with a lower MTU, as if PMTUD wasn't working. But, if I set the FTP server interface MTU to 1280, then the file is correctly transfered. Are there known problems with PMTUD ? Am I doing something wrong ? -- Mattieu Baptiste "/earth is 102% full ... please delete anyone you can."
