[isalist] RDP Black screen over gw-to-gw vpn (seems MTU problem)

From: "Daniel" <daniel@xxxxxxxxxxxxxxxx>
To: "ISAServerList" <isalist@xxxxxxxxxxxxx>
Date: Wed, 10 May 2006 23:05:32 -0300

http://www.ISAserver.org
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My on-demand dial gw-to-gw VPN between a ISA server 2000 on a Windows server 
2003 sp1 (RRAS), don't establish
a remote desktop connection (RDC), it shows a black screen and after 
"Connection to the remote computer was
broken caused by network error ...". The problem is related with w2003/sp1 
RRAS, causa i have other 4 same vpn
but with w2000 RRAS on the other end, an they work fine with RDP.

The wan link is a DSL(400/200kbps) but (ping -l 1472 -f dslmodem_pub_ip) work 
fine, the link accept MTU of
1500.

One a test client machine I reduce the LAN iface MTU to 1400, than RDC work 
trough the vpn between ISA and the
w2003/sp1 RRAS.
If I create vpn connection directly from the test client machine to the 
w2003/sp1 RRAS, and RDC rum ok, but
when I use the vpn that ISA establish with the same W2003/sp1 RRAS, RDC don't 
work.

Many articles talk about such problem with win2003/sp1 and all say to change 
the MTU size for PPP/vpn
connection on the client machine, eg. (Can't access RDC over VPN: 
http://www.chicagotech.net/Q&A/vpn47.htm),
but in my case the ISA establish this vpn connection (is gw-to-gw on-demand 
dial on the ISA box)

Trough all my vpns on ISA, including this with the win2003/sp1 RRAS, I can pass 
only 1372 withou fragmet, I
test with "ping 10.21.1.19 -f -l 1372"

I try to change the MTU for PPP(protocolMTU=1500) and VPN(TunnelMTU=1400) 
settings on register of the my ISA
and w2003/sp1 RRAS, but seems this apply only for client outbound vpn 
connections, not for the RRAS/Vpn
server. My ISA start the tunnel (he is the client), but the change don't solve 
the problem.

I try to change the MTU to 1400 and 1372(I this last have no sense) of 
respective demand dial connection on
ISA and on the w2003sp1RRAS, nothing.

My Isa2000 last update was the ISA2000-sp2, the win2000 have sp4 and all 
windows-update patches applied and
the w2003sp1 RRAS is too updated with asll windowsupdate patches.

Regards,

Daniel.

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[isalist] RDP Black screen over gw-to-gw vpn (seems MTU problem)

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