SSL VPN Performance is horrible using TCP or UDP

Question

We have 2 XG330 in HA, a 300Mbit connection and are using the SFOS 20.0.0 GA-Build222 firmware with Sophos Connect. 
 Using the SSL VPN with UDP we are seeing speeds of 3.6Mbit down and 6.9Mbit up. The Client has 100Mbit. 
 I've read a lot of different threads here regarding this issue, most of them are older than 2 years and most of them do not have an acceptable answer to this problem other than to switch the people who need a faster connection to IPSEC. 
 If anyone has any ideas I'll be glad to hear them.

Giridhar Katti · Answer

Hi Shawn Adams - Without setting up the SSLVPN tunnel between the client and the XG, can you configure a DNAt rule on the XGS and do the perf test(you can use iperf) to the server behind the XGS and check what's the speed we are getting ? 
 With this test - we will confirm, with the path being the same, what's the difference in throughput, with and without tunnel.

PhilippRusch · Answer

Hello Shawn, 
 this sounds like an MTU problem to me on either both links or at least one of them. 
 Normally, IPsec tunnels are more likely to have this kind of problem, but we should check this.

PhilippRusch · Answer

And, while working on this, you should check the debug setting to be turned off, as well.

SSL VPN Performance is horrible using TCP or UDP

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