VPN IP Address Conflict

[jshapiro]

For the second time in a couple of months, I've had a user call with an
IP address conflict. He is currently situated at a hotel, and his
hotel network connection gives him an IP of 192.168.2.x It just so
happens that one of our subnets is in the same range. When the VPN
tunnel is open, he can get to everything on our network but that
subnet. Although he gets correct DNS resolution from our DNS server,
anything bound for 192.168.2.x will route to the hotel network.
Unfortunately, our mail server and some other important resources, are
there.

It is obviously not practical for us to ask the hotel to change their
network addressing, and it isn't very easy for us to do it here. Short
of making a change at one end or the other, is there anything I can do
to work around this type of problem?

 

[Robert L [MS-MVP]]

You may want to modify the routing table to setup one to one traffic. this link may help,

VPN using same ip in the different subnet VPN server and client are using the same IP but in different subnets. Q: I have the following situation. I would like my home uses to connect to the ...
www.chicagotech.net/Q&A/vpn38.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
For the second time in a couple of months, I've had a user call with an
IP address conflict. He is currently situated at a hotel, and his
hotel network connection gives him an IP of 192.168.2.x It just so
happens that one of our subnets is in the same range. When the VPN
tunnel is open, he can get to everything on our network but that
subnet. Although he gets correct DNS resolution from our DNS server,
anything bound for 192.168.2.x will route to the hotel network.
Unfortunately, our mail server and some other important resources, are
there.

It is obviously not practical for us to ask the hotel to change their
network addressing, and it isn't very easy for us to do it here. Short
of making a change at one end or the other, is there anything I can do
to work around this type of problem?

 

[Phillip Windell]

If Robert's article doesn't help then you would need to re-address your own
LAN. You should never use the "lower" addresses to start with,...you are
just asking for this to happen. Raise the third octect to at least over
10,...I would suggest even over 25.

 

[jshapiro]

I browsed through the web site you linked, and it was informative, but
it didn't give me an example of how to set up the routing tables. I
assume that this is an entry that must be made on the client's
computer. Can you point me to an example?

 

[Robert L [MS-MVP]]

Remember this is one to one route meaning the VPN client access to only one remote computer. If you want to two remote computers, you need to add two route. for example, to access a computer with IP 192.168.2.10 from a computer with IP 192.168.2.11, you use this command:

route add 192.168.2.10 mask 255.255.255.255 192.168.2.11.

More details can be found this page,

Routing Route command and examples Routing issue if the LAN and VPN are in different ... Route command and examples. PRINT Prints a route - route PRINT 157* . ...
www.chicagotech.net/routing.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
You may want to modify the routing table to setup one to one traffic. this link may help,

VPN using same ip in the different subnet VPN server and client are using the same IP but in different subnets. Q: I have the following situation. I would like my home uses to connect to the ...
www.chicagotech.net/Q&A/vpn38.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
For the second time in a couple of months, I've had a user call with an
IP address conflict. He is currently situated at a hotel, and his
hotel network connection gives him an IP of 192.168.2.x It just so
happens that one of our subnets is in the same range. When the VPN
tunnel is open, he can get to everything on our network but that
subnet. Although he gets correct DNS resolution from our DNS server,
anything bound for 192.168.2.x will route to the hotel network.
Unfortunately, our mail server and some other important resources, are
there.

It is obviously not practical for us to ask the hotel to change their
network addressing, and it isn't very easy for us to do it here. Short
of making a change at one end or the other, is there anything I can do
to work around this type of problem?

 

[jshapiro]

How does this 'route add' prevent the client from routing to an IP on
the hotel subnet and allow him to route to an IP on our office network.
Seems like there'd still be confusion with this.