Here’s the command to install the 3 packages:

sudo apt-get install network-manager-pptp network-manager-vpnc network-manager-openvpn

I have no idea why Ubuntu doesn’t include these packages by default. Looks like a great many people are having this issue: https://bugs.launchpad.net/ubuntu/+source/network-manager-pptp/+bug/107738

The easiest way to do this is to have the network manager handle it all by adding a setting in the network manager like so:

Click on the network manager icon then “VPN Connections” and the following menu should appear: Click “Configure VPN”.

Click the VPN tab. The VPN you have already created should appear in the list. Click your VPN and then click edit.

Another window should appear, click the “IPv4 Settings” tab. Then click the “Routes…” button.

Now you need to add a route so your computer can talk to other computers on the VPN. In this case I have added the address as 192.168.10.0 as all computers on the office network have an IP that begins with “192.168.10″ and a netmask of 255.255.255.0. The gateway is the IP of my home router, in this case my home router is “10.11.12.1″.

At this point it’s also worth mentioning as a side note that if “Use this connection only for resources on its network” is NOT ticked then all of your regular internet traffic will go via the VPN and not just when you want to access something on VPN like shared files and folders. This would really slow down your internet access. I personally would have this ticked.

And there you have it, that will now allow your computer to talk to other computers on the office/remote network.

For those of you who want a more hands on approach and really want to see whats going on behind the scenes (everyone else stop reading here):

Run the route command to view the routing table:

route

This is the route table with the missing route:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   my.router       255.255.255.255 UGH   0      0        0 eth2
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         my.router       0.0.0.0         UG    0      0        0 eth2

The network manager automatically adds the correct route to the routing table when the VPN connection is created. You can achieve the same result with the following command. In this case we are using the network range 192.168.10.*:

sudo route add -net 192.168.10.0/24 ppp0

Now check the routes table again:

route

And here we have a route that allows us to access computers on the remote network:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   10.11.12.1      255.255.255.255 UGH   0      0        0 eth2
192.168.10.0    *               255.255.255.0   U     0      0        0 ppp0
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         10.11.12.1      0.0.0.0         UG    0      0        0 eth2

http://tipotheday.com/2007/11/28/connect-to-windows-vpn-server-pptp-with-ubuntu-gutsy/

Unfortunately when using the network-manager-pptp package there is a bug with one of the network packages that prevents anyone with a static IP from succesfully connecting to a VPN server. When you left click your network icon you should see one of your network connections as selected. If they are all greyed out then you will suffer from this VPN issue. Unfortunately at the time of writing there is no fix other than to set your network connection from a static IP to roaming mode. Some people have suggested that Interpid Ibex will have a fix for this problem.

The bug tracker for this can be found at https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/116274

Does anyone know a better work-around for this?