SSL VPN Connection Slow (warning large screenshots)

Hi All,


I am experiencing very slow SSL VPN speeds (10x slower than internet upload speed, 70x slower than internet download speed). I read almost all posts I could find, but no solution worked.

Can you help me out?





Here is what I have as a setup:

Hardware: Qotom q355g4, 6GB RAM, 120GB SSD, (Sophos XG runs directly on the hardware)

Internet connection:

Resource usage:

Transfer speeds on the VPN (both download and upload):

SSL VPN UDP Settings:


VPN to LAN  rule:

  • A couple of things to try might be to disable compression and/or switch Application Control to "none" and see if that makes any difference. 

  • When you use UDP it may be wise to decrease the MTU on your client to 1312. This depends on your ISP.

  • In reply to Bill Roland:

    Hi Bill, I can confirm these modifications don't work.

  • In reply to Weatherlights:

    Hi Weatherlight,

    When I am running a ping both on LAN and on remote via SSL VPN towards server on LAN, I get the following:

    C:\Users\user_name>ping -f -l 1382

    Pinging [] with 1382 bytes of data:
    Reply from bytes=64 (sent 1382) time=9ms TTL=54
    Reply from bytes=64 (sent 1382) time=9ms TTL=54
    Reply from bytes=64 (sent 1382) time=10ms TTL=54
    Reply from bytes=64 (sent 1382) time=13ms TTL=54

    Ping statistics for
        Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
    Approximate round trip times in milli-seconds:
        Minimum = 9ms, Maximum = 13ms, Average = 10ms

    I am on cable and not PPOE (DSL)


    Without modifying anything on the server, I added the following on the client .conf file:

    tun-mtu 1382

    no  change.

    I then tried:

    tun-mtu 1382
    mssfix 1342

    no change.

    No change either for: tun-mtu 1312 as you suggested.

    Maybe I am doing things wrong.

    Any document detailing how to modify the MTU on SFOS XG for SSL VPN in UDP mode?