Is it possible to let 2 vtp domains communicate with each other?
We have one network devided over 40 locations in one city. in half of the network some vlans excist and in the other half other vlans excist. There's no need that the whole network nows about all vlans.
Anyone has some answers or solutions?
Assuming that you will use layer3 to interconnect both networks, there will be no issues with vtp. This is also the recommended method to do this.
The router may very well be a layer3 switch but you must use an access-port (swichport mode access) to connect to the layer2. Using a trunk-port will get you into trouble while the switch will then have a potential problem with the vlan ID's in the network that does belong to the other vtp domain.
If you are talking about data communication between 2 different VTP domains YES it will work but if you are talking about VLAN synch between 2 different VTP domains NO that's not possible.
VTP function is just to have vlan information synch between all your network devices so that you need not configure VLANS manually on all your devices and is not aat all concerned with data communication between devices.