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VPN connection fails occasionally !

Posted on 2006-05-30
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Last Modified: 2010-04-12
What happens is that when trying to dial VPN from one of the PC's on the LAN, i succeed occasionally to establish the connection, but in most cases connection fails and what i feel is that the time out value of the VPN server is not letting me to accomplish the process successfully since it works once and fails most of the time especially when the LAN's bandwidth is highly utilized ( congestion )........Is it that the VPN server on the other side of the world requiring authentication in a short period of time that i cannot reach due to the lack of internet bandwidth shared on the network ??? Is there any other reason that could be behind the occasional failure ?? What are the initial steps, or any workaround on the clients PC to improve VPN connectivity response ??

Please advice.

P.s ( when i used a separate ADSL line ( no bandwidth shared with other PCs) i never faced a single login failure to the same VPN server, from same PC )
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Question by:adelf
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Expert Comment

by:Rob Williams
ID: 16791737
It can be a poor or slow connection. As a test when you are able to log on try a ping command to a device on the remote network through the VPN tunnel. A VPN should have a response time of 125ms or less to be reasonably stable. A good connection is usually 50ms or less.

It can also be to high an MTU value. (Maximum Transmission Unit) for the connection. Have a look at the following sites for an explanation of the problem, how to test, and how to change. If you wish to make changes, it should be set on the connecting computer ant it's local router if possible.
http://www.dslreports.com/faq/7752
http://www.dslreports.com/faq/5793
http://www.chicagotech.net/vpnslow.htm
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Author Comment

by:adelf
ID: 16801571
Ok i talked to the Security administrator and he required having the following protocols and ports opened and enabled to access his vpn server and get through his firewall :

PPTP 1723
Telnet 259
Protocol GRE 47

Today when trying to dial vpn from one of the concerned PC's, i got the authentication window, entered the correct username and password, waited for sometime, seemed to be working but after about 10 secs of negociations, connection failed !!!!

My question now is should those protocols have INBOUND and OUTBOUNT access ??? because what i believe is that our firewall passes only the Outbound packets....Aren't the mentioned protocols enabled by default in the 501 pix firewall ? What should be done ??
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Rob Williams earned 500 total points
ID: 16806541
By default, all out going ports are open and all incoming ports are closed.
 
Perhaps we need a little more information. Could you outline your VPN configuration, from where you are trying to establish the connection and what error message/# you receive when the connection fails. i.e is this a VPN software client to VPN router connection, site to site, or client to VPN server such as a Windows VPN server? Also what make router and VPN client are you using? Sounds like a Cisco software client to Cisco PIX VPN ?
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Assisted Solution

by:rsivanandan
rsivanandan earned 500 total points
ID: 16827455
Try to reduce the MTU size on the box and see if that makes any difference. If this is a Cisco VPN Client, you will have an option for reducing MTU with that itself (Programs Menu). Reduce it to 1300 and see if that makes any difference.

Cheers,
Rajesh
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Author Comment

by:adelf
ID: 16831343
Robwill,
Its a customized version of client to server VPN connection ( used by a certain company ) and not a cisco or windows client......the error was in german but according to what i was told, it means firewall error, please check your firewall settigns, and the message appeared after the authentication level was accomplished.....

 Rajesh,
Unfortunately,its not a cisco client and i didnt find any option to decrease the MTU value on that VPN client software !

Any other hints ?
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Expert Comment

by:rsivanandan
ID: 16831407
I'm not quite following here, if it succeeds occasionally then how come there are no firewall problems ?

To reduce the MTU size on the windows box, you can find the information here;

http://www.winguides.com/registry/display.php/280/

Cheers,
Rajesh
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Expert Comment

by:Rob Williams
ID: 16835131
adelf , where you can establish a connection and not maintain it, it does sound like it may be an MTU issue. See if you can adjust on the PC and it's local router using the instructions I provided in my first post or using rsivanandan 's link, and see if there is any improvement. I am assuming this is not a satellite based connection ??
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Expert Comment

by:rsivanandan
ID: 17019994
Interested ??

Cheers,
Rajesh
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Expert Comment

by:Keith Alabaster
ID: 17020021
lol @ Rajesh. Lets see if the asker is as well......
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