Recently had a problem with a Cisco Router Failover pair causing me some grief where when you download a large file it was just cutting out or stopping. I tried a few attempts and even tried downloading on our own firewall and the download worked fine so I knew there was no problem at the remote end (Microsoft)

Was trying to download SQL 2012 Express at the time and this kept happening:

CiscoRouterDownload-1

First thing I done was open an ssh  session with the Router and enabled terminal monitor:

Log in and type:

Once that was done I noticed quite a few errors like this appear:

%FW-4-TCP_OoO_SEG: Dropping TCP Segment: seq:3558911335 1500 bytes is out-of-order; expected seq:3558888055. Reason: TCP reassembly queue overflow – session 10.0.X.X:52435 to XX.XX.XX.XX:231424

I added this command to global config mode:

All the command above does is increase the size of the tcp queue which has solved this problem.

Downloads are now working perfectly!

One thought on “Cisco Router – Slow / Dropping Internet Downloads

  1. Worked for us! (actually Cisco was reviewing the issue and wouldn find the cause after two days)

    We used a smaller value, it was enough to use 128 instead of 1024 (the default is 16)

    Regards

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