can't connect to vpn if a service listens on port 1723

  • Thread starter Thread starter ggo98
  • Start date Start date
G

ggo98

Hello,

I have a win2003 server with VPN service enabled, and I can
successfully connect to it from a winXP workstation.

However, there's a really strange thing I do not understand:
if a service listening on the port 1723 is started on the winXP
workstation (not the win2003 server of course), then it is not possible
to connect any more to the win2003 server (????) - an error is
returned... (800 or 721)

does someone know why. I really don't understand what can be the reason
explaining this behaviour.

Thanks in advance for any help

Regards,
Olivier.
 
You can use netstat to find out which application is using the port 1723.

How to find open ports on a computer To display all open ports, open DOS command, type netstat and press Enter. ... To see what ports your computer actually communicates with, use netstat -an ...
www.howtonetworking.com/command/openport1.htm


Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on http://www.ChicagoTech.net
How to Setup Windows, Network, VPN & Remote Access on http://www.HowToNetworking.com
Hello,

I have a win2003 server with VPN service enabled, and I can
successfully connect to it from a winXP workstation.

However, there's a really strange thing I do not understand:
if a service listening on the port 1723 is started on the winXP
workstation (not the win2003 server of course), then it is not possible
to connect any more to the win2003 server (????) - an error is
returned... (800 or 721)

does someone know why. I really don't understand what can be the reason
explaining this behaviour.

Thanks in advance for any help

Regards,
Olivier.
 
hi,

thank you for your answers.

well I actually do know which service listens on port 1723.
What I don't get is why does the VPN connection to the win2003 server
fails if the service listening on port 1723 is started on the winXP
client ?

Thank you,
regards,
Olivier.
 
I would imagine that that service is holding the port hostage basically and
not letting the VPN connection use it. This is not uncommon.
 
Hi Scott,

no, this is not the problem I believe: the service listening on the TCP
port 1723 is started on the client side, not on the win2003 server
side...
or there's may be something I don't know...
does the client need to listen on port 1723 at some point of the
negociation ?
AFAIK, the client connects on port 1723 on the server, right ? so why
would a service listening on port 1723 on the client side be a problem.

Regards,
Olivier.


Scott Harding a écrit :
 
That's what I meant. The client has some issue. I don't know of any service
that would be listening. The VPN doesn't grab the port until you start the
connection. Do the netstat command on the client to see what is holding the
port.

--
Scott Harding
MCSE, MCSA, Net +, A+
MVP - Windows Server Networking

Hi Scott,

no, this is not the problem I believe: the service listening on the TCP
port 1723 is started on the client side, not on the win2003 server
side...
or there's may be something I don't know...
does the client need to listen on port 1723 at some point of the
negociation ?
AFAIK, the client connects on port 1723 on the server, right ? so why
would a service listening on port 1723 on the client side be a problem.

Regards,
Olivier.


Scott Harding a écrit :
 
Hello Scott,
you were right, the port 1723 is used after the VPN connection is
established...
Every thing's clear now.
Thank you for your help,
kind regards,
Olivier.

Scott Harding a écrit :
 
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