kernel-packages team mailing list archive

[Jose Manuel Pasamar <jpasamar@xxxxxxxxx>]

We have tested the kernel 3.19-rc7 and found some improvements.

Communication does not stop and the file can be finally downloaded, but
it still takes a long time.

We have tested a 100 MB file in an Ubuntu server with kernel 3.19-rc7 across the Cisco firewall changing sequence numbers with following results:
- With TCP SACK disabled (sysctl -w net.ipv4.tcp_sack=0)             62 seconds
- With TCP SACK enabled (default configuration)                         462 seconds

It seems that, even though the communication is not completely stalled
with this kernel version, the problem is not solved yet.


** Tags added: kernel-bug-exists-upstream

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https://bugs.launchpad.net/bugs/1388786

Title:
  TCP stale transfer with erroneous SACK information

Status in linux package in Ubuntu:
  Incomplete

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

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