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[Launchpad Bug Tracker <1388786@xxxxxxxxxxxxxxxxxx>]

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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

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Invalid

-- 
TCP stale transfer with erroneous SACK information
https://bugs.launchpad.net/bugs/1388786
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