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Host_Error: CL_ParseServerMessage: Illegible server message
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When i connect via any proxy to wargamez.dk or quakeworld.fi i get
error message showed up and disconnect. Havent seen such trouble on other
servers, but i didnt checked them all.

Looked serverinfo and see no difference with other servers (ie pangela.se), where this
problem does not appear.

Anyone have idea how to solve that problem?

P.S. I use /setinfo MTU 1400

Why are you fibbling with the MTU?

I use vpn over ethernet, that repack standart packet size of 1500 bytes with a 1400 real data and ~100 vpn service data.
Every time when i get statistics after match or doing cmd dlist, i get asynchronisation with server, which needs reconnect.
/setinfo MTU 1400 helps almost always.

It is a bug in mvdsv, you can use ezquake with workaround about broken mvdsv. Well, mvdsv is fixed too, just servers are not updated.

And yes, /mtu is quite useful in case of vpn connections, I see time to time hanged players after match end, they have to /reconnect but /mtu effectively fix it.