RDP sessions freeze when connection to local network over Sonicwall VPN

Barry Fields
Barry Fields used Ask the Experts™
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I have several users that work remotely and connect to the local network over a Sonicwall VPN, both the group VPN client and the SSL VPN appliance are exhibiting the same symptoms . When a user is in an app (Office or Adobe acrobat) the RDP client freezes
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nociSoftware Engineer
Distinguished Expert 2018

Commented:
If the RDP gateway protocol is used there may be a problem with proxy traffic. (or traffic that does content validation foor HTTPS).

RDP (gateway) uses a request for 1MB to wait for the remote site...  If the proxy wait for this to complete BEFORE passing on the data then there will be no data.
Anything proxying https gateway RDP traffic needs to allow for partial traffic.... and suddenly aborted IO's are not really abortd IO's just start for the next request.
So even "failed" data needs to be passed on.
Barry FieldsIT manager

Author

Commented:
I am not sure I understand your answer but we are not using a proxy
nociSoftware Engineer
Distinguished Expert 2018

Commented:
Do you use DPI on https? If yes then you are proxying implictly (you need to decrypt the traffic, then reencrypt again to send on),
The DPI part acts like it is a transparent proxy.

So A firewall MAY introduce a "hidden" "transparent" proxy.  (It is not really transparent as the  server part of a link gets a new certificate).
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Barry FieldsIT manager

Author

Commented:
I don't think this applies as I see the problem with the Group VPN which doesn't use https
nociSoftware Engineer
Distinguished Expert 2018

Commented:
RDP Gateway protocol uses HTTPS...  (RPC calls accross HTTPS), unless you are using the classic Port 3389 protocol. (Which should not suffer from the same problems).
Then are there filters on port 3389/TCP?
Barry FieldsIT manager

Author

Commented:
We are using 3389 and there should be no filters. We have turned off local printing on the RDP session and so far 1 hour no freezing
nociSoftware Engineer
Distinguished Expert 2018

Commented:
That should be something from within the protocol...  and not be influenced by the VPN tunnel or firewall, unless is causes massive traffic and packet retransmits and drops....  Still should not hang, just get slow...
IT manager
Commented:
Problem cleared on its own

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