Package: linux-2.6 Version: 2.6.18-8 Severity: normal Symptoms: After a few weeks/months of uptime, my IPv6 machines whose IPv6 "first hop" link MTU is more than the minimum (1280) stop reacting to ICMPv6 "too big" packets and keep sending TCP packets above the MTU of the path to other hosts.
Expected behaviour: After getting an ICMPv6 "too big" packet, send only packets smaller than the MTU in given in that ICMPv6 packet to this host. Analysis: I get the impression that the table where the kernel keeps the PMTU to the IPv6 hosts it communicates with overflows over time, after a few weeks or months of uptime. It looks like entries in that table expire (because I do get the too big packets problem with hosts my hosts communicate with a lot, they certainly were in the table in the past), but that the place taken by expired entries is not freed up. Thus the table doesn't get new entries added when the ICMPv6 "too big" packet comes in and the TCP stack doesn't go back to smaller packets. The symptoms seen by the users is that e.g. a SSH or SMTP connection gets established OK, but once they start doing something "big" with it (like the DATA phase of the SMTP dialogue or doing an ls of a big directory in a ssh session), the connexion freezes. Once that effect kicks in, it affects all new IPv6 connections/hosts. A tcpdump shows that ICMPv6 "too big" packets come in, but that my host keeps sending too big packets. A reboot cures it. I vaguely remember that the first time this happened, I found some statistics file in /proc/ or /sys/ where one line said some table had 4095 entries, which led me to this analysis. Alas, when it happened again I could not remember what file that was and can't find it again now. I didn't report it at the time because the kernel run by this machine is rather old. But now it happened on a machine running 2.6.18-3-amd64, and "echo 8192 > /proc/sys/net/ipv6/route/max_size" seems to have helped the problem. -- System Information: Debian Release: 4.0 APT prefers unstable APT policy: (500, 'unstable'), (1, 'experimental') Architecture: amd64 (x86_64) Shell: /bin/sh linked to /bin/bash Kernel: Linux 2.6.18-3-amd64 Locale: LANG=fr_LU.UTF-8, LC_CTYPE=fr_LU.UTF-8 (charmap=UTF-8) -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
