Intermittent xfreerdp hang only through VPN

[Younes Manton]

On Wed, Sep 2, 2015 at 1:46 AM, Younes Manton <younes.m at gmail.com> wrote:
> On Tue, Sep 1, 2015 at 7:00 PM, Stuart Henderson <stu at spacehopper.org> wrote:
>> On 2015/09/01 16:04, Younes Manton wrote:
>>> Hi,
>>>
>>> I've had this problem for at least a couple of years. Whenever I
>>> connect to a Windows machine via xfreerdp over my work place VPN the
>>> xfreerdp client inevitably hangs. Occassionally SSH sessions will also
>>> hang, but this happens much less often. I never see either problem
>>> when not connected over VPN.
>>>
>>> I normally run OpenConnect via Network Manager, but I recently ran it
>>> on the command line with -v to watch the output. As best as I can tell
>>> the hangs always follow a CSTP rekey and the only thing that's
>>> different from the usual is that these lines begin to appear:
>>>
>>> Send CSTP Keepalive
>>> Send CSTP DPD
>>> Got CSTP DPD response
>>>
>>> They seem to stop being emitted once I kill the unresponsive xfreerdp client.
>>>
>>> On the Windows side I see the following in the Event Viewer every time
>>> xfreerdp hangs:
>>>
>>> The Terminal Server security layer detected an error in the protocol
>>> stream and has disconnected the client. Client IP: <my IP>.
>>>
>>> Anything I can do to debug this?
>>
>> Try reducing the mtu requested (openconnect's -m flag).
>>
>
> Thanks. Seems like the server doesn't allow anything outside of
> 1280-1300, the values I pass to -m are clamped to that range. Neither
> helps my problem.

So I tried using ifconfig to change the MTU on the vpn interface
rather than relying on openconnect; lowered to 1100, but that didn't
help. Is there anything else I can do to debug this?