Question : Problem: VPN configuration

Please assist, I need to setup a VPN network between 2 Sites, both sites got the firewall but difference brand. My HQ host a Zyxel Zywall 5 & subsidary host a Soekris Engineering net4801 firewall.

Now I plan to configure a VPN which connect from Susidiary to HQ, so what configuration needed to accomplished the mission? Any port forward needed? Is it MUST get a fixed IP? How many concurent connection If only one fixed IP for the VPN?

Thanks for help!

Answer : Problem: VPN configuration

The VPN tunnel can come up but no data would flow over the VPN tunnel, because in this case the device cannot decide if the packet is intended for the local or for remote subnet; and the default decision then is to route all traffic to the internal network.

Let me take an example:
Let's site A has IP 192.168.0.1-192.168.0.100; and site B has 192.168.0.150-192.168.0.250
In both above cases there is no IP overlap and the IP subnet is 192.168.0.0./24
However the device at location A knows that all the packets for 192.168.0.0/24 exist behind it and so does device B; so no packet for 192.168.0.0/24 subnet would be sent over the VPN in this case.

To eliminate this problem, either simply change the IP subnet at one end, say at site B to 192.168.1.0/24
or in our example we can put them in different subnets as below:
Site A: 192.168.0.0/25; valid IPs: 192.168.0.1-126; broadcast IP: 192.168.0.127
Site B: 192.168.0.128/25; valid IPs: 192.168.0.129-254; broadcast IP: 192.168.0.255

Thank you.