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Slow download speed or large files cannot be downloaded in InterScan Web Security Virtual Appliance (IWSVA)

    • Updated:
    • 9 Sep 2018
    • Product/Version:
    • InterScan Web Security Virtual Appliance 6.0
    • InterScan Web Security Virtual Appliance 6.5
    • Platform:
    • N/A N/A
Summary

The download speed is slower than the expected/assigned bandwidth internet speed or the download of some large files (more than 2GB) cannot be completed the first time a user tries to download them.

Details
Public

The window scale option is used only during the TCP 3-way handshake and many routers and firewalls re-write the window scaling factor during a transmission. This causes the sending and the receiving sides to assume different TCP window sizes; the result is non-stable traffic that is very slow.

 

However, the TCP window scaling option may have some side effects. Since many routers and firewalls do not properly implement TCP Window Scaling, it can cause a user's internet connection to malfunction intermittently.

Because of that, it is not enabled by default in IWSVA. You can keep it enabled if no other issue (i.e. access, download) occurs, however, it is recommended to monitor the behavior afterwards and to revert it to the initial settings if needed.

To verify if the situation has improved, we can set the IPv4 TCP Window Scaling parameter from 0 to 1:

  1. Connect to IWSVA directly or via SSH (for example via Putty) as "root".
  2. Open the file /etc/sysctl.conf
  3. Find and change the following parameter to 1:

    net.ipv4.tcp_window_scaling=1

  4. Save and exit.
  5. Run the command "sysctl -p"
Premium
Internal
Rating:
Category:
Configure; Troubleshoot; Deploy
Solution Id:
1118136
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