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I'm trying to configure VPN access. On the office network, IP address are 192.168.1.x.

I configured my laptop with VPN properties (I work on Mac OS X.6).

VPN connection works everywhere. But if both network (office and laptop) have the same IP range, I am able to connect, but have a problem accessing a machine by its IP address on the office network.

I think that I must configure something on router but What?

Thanks for any help.

Isabelle

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migrated from stackoverflow.com Jun 6 '13 at 0:01

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3 Answers 3

I think it would be easier to change the IP range of your home network than to try and change your office network. The two networks (office and home) need to have different network address ranges otherwise, as Bob indicates above, routing of network packets get confused (this refers to the routing software on your computer as well as your network routers).

Most home routers come configured to use a 192.168.x.x address range; typically, they are automatically configured for the 192.168.1.x range. The easiest thing to change is your home network so it uses a different 192.168.x.x range of addresses than your office network. For example, the 192.168.2.x range of addresses.

How you make this change in your home router depends on the brand and model of your router. On most routers, you can login directly to the router's admin page by pointing your browser to the x.x.x.1 address (in your case, try typing

http://192.168.1.1/ 

into your browser's URL or address bar) when you are at home and are not using the VPN (turn the VPN off). You will probably have to provide a userid and/or password. If you don't know the userid and password you can search the web for the default values (include your router brand and model number in the search). If the defaults don't work and you can't remember what they were changed to you'll have to hard reset the router to get the defaults back (again, search the web for instructions specific to your router).

Once you have successfully logged into the router's admin pages, there will likely be a setup or basic setup page (probably the first page you see) or a LAN setup page. What you are looking for is a place where you can specify the local network IP address. In your case, you should find this field filled in with 192.168.1.1 and there will probably also be an IP subnet mask field next to this, with a value of 255.255.255.0. Change the IP address to something like 192.168.2.1 or 192.168.3.1, etc. Anything that is different than the IP address range that is used at work. Leave the subnet mask set to 255.255.255.0.

After you've made this change you should reboot your router (or power it down, wait one minute and then power it up), and you should also reboot any machines that are connected to your home network after you've reset the router. Your machines need to get assigned new IP addresses in the new address range that you setup in your home router or they will get confused and won't work on the network.

If any devices on your network have statically assigned IP addresses you will have to change those manually. If you do not know if you have a device with a statically assigned address it means you probably do not have any devices with statically assigned addresses.

Hope that makes things work better!

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p.s. It is unfortunate that your work network is setup to use the 192.168.1.x address range, since this is so commonly used as the default by so many routers. This means, for example, that if you are using the wifi in a Starbucks or hotel lobby and their local address range is also 192.168.1.x you are going to have troubles when you connect to your work network over the VPN. Check to see if you can "disable local network access" in the VPN settings, this might help where the local and remote networks share the same address range. –  Paul Fischer Jun 6 '13 at 16:15

You will need to alter the range of one of your networks.

The problem arises because your laptop needs to know how to route your traffic.

For example:

If your office network was 192.168.1.x and your server was 192.168.1.1. If your laptop was connected to a network where the network was 192.168.1.x and the router was 192.168.1.1.

When you tried to talk to the server the most likely decision your laptop will make is that 192.168.1.1 is on the local network so just send the request out the local Ethernet (or wireless) so the traffic will hit your router which assumes the request is for it has it has the same IP address.

Alternatively if you somehow managed to convince your laptop that 192.168.1.1 was through the VPN then your laptop would try and connect over the VPN which means that it would try and send the VPN packet to your public IP address, which as far as it is concerned is via the gateway on 192.168.1.1 which is over the VPN so the VPN will never get there.

The ideal solution would be if you can change your office network to one that is less likely to conflict default network addresses of ADSL routers and public WIFI.

The are a whole host of private IP addresses you can use.

10.0.0.0 - 10.255.255.255 
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255 

The only other alternative you could risk if the specific IP addresses of the office machines you are trying to reach are not going to conflict with your local net would be to have more specific routes applied over the VPN - e.g. 192.168.1.241 netmask 255.255.255.255. This would work until your local router handed that IP out to your machine or you needed to talk to a machine on your local network with that address.

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Thanks for this answer. But it's impossible to change office adress because if not internet connection doesn't work, box provider is lock. So good idea, I try to do but impossible. Is it possible to create specific rules on router (like NAT) to give on laptop adresses on different ip range even if on connection start range is same? –  Flex60460 Jun 4 '13 at 9:31
    
@Flex60460 Can you manage the VPN address ranges and what is your VPN box –  Bob Vale Jun 4 '13 at 16:04

I bring my air port express and connect the airport express to the hotel wired network. Then I am in control of the ip address range used by airport express. Besides that, it is often faster. I can connect all of my devices without configuring them to a new network.

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