I can confirm this bug with the 3.13 kernel shipped with Ubuntu 14.04. The 3.2 kernel shipped with Ubuntu 12.04 did not have the problem, all download were succeeding. The problem started after upgrade to 14.04. The problem also solved after downgrading the kernel to 3.2 by downloading the latest 12.04 (Linux 3.2) one from the PPA.
Disabling TCP SACK also resolved the issue. I also tried newer PPA kernels, at least the next one for release with next Ubuntu Update (3.14) does not solve the problem yet. In our case the problems happens mostly with far-away or slower DSL connections, trying to download large files from our webserver. The download starts fine, but suddenly slows down to 0 bytes/sec. It then sometimes recovers, but fails again after a short while. The tcpdump showed, that the client is sending SACKs over and over, but the Ubuntu kernel does not understand them. In our case we also have Cisco hardware inbetween. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1388786 Title: TCP stale transfer with erroneous SACK information Status in linux package in Ubuntu: Confirmed Bug description: Cisco PIX/FWSM changes TCP sequence numbers but doesn't change numbers in SACK TCP options. When this erroneous information comes to Linux server there is some corruption in TCP stack in some circunstances with CUBIC TCP congestion algorithm and transfer stales. Problem can be reproduced in Ubuntu Server 14.04 when a Cisco FWSM is changing sequence numbers (default configuration) and a big file (30MB, for example) is being transfered. Can be solved deactivating SACK: sysctl -w net.ipv4.tcp_sack=0 We have solved it also with this configuration: sysctl -w net.ipv4.tcp_congestion_control=reno sysctl -w net.ipv4.tcp_frto=1 sysctl -w net.ipv4.tcp_early_retrans=1 We can also fix it by changing firewall configuration. Find attached a wireshark capture where you can see at 16613 frame how client requests segment 853521869 and server (158.42.250.128) resends again a previous segment for 87 seconds until it stops transfer. Thanks To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1388786/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
