MTU Settings for VPN

ginggs

ginggs

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Hi, just wondering if someone here has any suggestions on the following.

I've been struggling yesterday and this morning to work on a remote Windows server for a client. The procedure I usually follow is to establish a VPN connection to their server's public IP address and then an RDP connection to their server's private address.

I am able to establish the VPN connection over PPTP without any problem and am able to ping their server's private IP address and can even access Windows shares. When I try and establish the RDP connection I get a black window of the size I specified and then after 30 seconds or so I get a message that the connection was terminated.

I have tried on my Windows XP SP3 workstation and also on a notebook running Ubuntu Netbook Remix 9.10 (I used KVpnc for the VPN as I couldn't get Network Manager to work). I have tried disabling my firewall to no avail.

This morning I took my notebook to their offices and was able to connect over their ADSL connection without changing any settings.

Could it be something on iBurst? I can't think how iBurst could affect traffic over a PPTP connection, but that is what it seems like.
 
I had a similar problem once and I just lowered my routers MTU settings. I have not used iburst now for a few years so not sure if that will solve your problem.
 
I'm not using a router, my iBurst modem is connected to my Windows box via USB and shared via ICS. How can I set the MTU for a USB connection?
 
ginggs said:
Hi, just wondering if someone here has any suggestions on the following.

I've been struggling yesterday and this morning to work on a remote Windows server for a client. The procedure I usually follow is to establish a VPN connection to their server's public IP address and then an RDP connection to their server's private address.

I am able to establish the VPN connection over PPTP without any problem and am able to ping their server's private IP address and can even access Windows shares. When I try and establish the RDP connection I get a black window of the size I specified and then after 30 seconds or so I get a message that the connection was terminated.

I have tried on my Windows XP SP3 workstation and also on a notebook running Ubuntu Netbook Remix 9.10 (I used KVpnc for the VPN as I couldn't get Network Manager to work). I have tried disabling my firewall to no avail.

This morning I took my notebook to their offices and was able to connect over their ADSL connection without changing any settings.

Could it be something on iBurst? I can't think how iBurst could affect traffic over a PPTP connection, but that is what it seems like.
Click to expand...

RDP over PPTP vpn works fine.I go thru a router and have'nt touched the MTU on my router.Currently on a 1GB iburst package.
 
Please set the MTU down to 1364.

Try that and let us know.


Thanks
 
biena said:
TCPOptimizer is for network, check if it works for usb also ?
Click to expand...
iBurst said:
Please set the MTU down to 1364.
Click to expand...
Thanks for the suggestions. I'll try them tonight.

I also found this in the Connectivity and Coverage section of the iBurst FAQs:
How can my MTU settings improve iBurst performance?
MTUs are critical when using iBurst. Connectivity in a networked environment requires MTUs set on the router and the network interface ports.
iBurst is based on PPPOE & default Windows MTU settings of 1500 can't be used, and should be adjusted, even if problems are not experienced.
Correctly set MTU will prevent packet fragmentation resulting in degraded connectivity. The recommended MTU for iBurst is 1392. For stand alone USB or PCMCIA please set the Dial Up Ras MTU to 1392 . Set MTU for VPN to 1364.
Click to expand...
 
I found that often the MTU size on the router at the client also needs to be dropped.

On a technical level, the MTU issue is one of the most irritating properties of the iBurst system.
 
Following Microsoft's instructions, I modified the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0 as follows:

Changed the value 'ProtocolMTU' from 1400 to 1392
Added the value 'TunnelMTU' equal to 1364

I was then able to establish the RDP over VPN connection on both Windows and Linux with Comodo firewall on Windows disabled.

To get it to work with Comodo firewall enabled I also had to disable 'Block Fragmented IP datagrams' in Firewall Tasks / Advanced / Attack Detection Settings / Miscellaneous.

I think some further experimenting is required; I now have a new data allocation on Vodacom so I have another connection with which to compare.
kaspaas said:
On a technical level, the MTU issue is one of the most irritating properties of the iBurst system.
Click to expand...
Why doesn't the iBurst setup program set these values?
 
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