Consider setting up a IP address reservation on a LAN for the purposes of securing IP addresses to particular PCs/workstations that will be hosting servers/services.
Take as an example, the following scenario:
On Netgear routers two particular screens are used to configure what is necessary in this situtation: the LAN IP Setup screen and the Port Forwarding screen.
First dealing with the LAN IP setup.
On LAN IP setup menu reserve IPs addrs for each of PC1 - PC4 (if considered necessary). It may in fact only be necessary for PC1 and PC2 (in the example) as they are the only ones hosting a service that may need to be accessed from externally.
This can be achieved by using one or other of two methods.
In the first method case the router may be allocating IP adds in a resticted range, say up to .51. In this case you could get away with doing nothing in the router at all and simply manually assigning IP addresses in individual PCs to lie outsite the router issued IP address range. As per the example assign PC1 to 192.168.0.101, PC2 to 192.168.0.102, etc etc. This is what I described as method i) in my initial email.
Alternatively, if you do not want to assign IPs manually in each PC you can configure the router to issue the IP addrs to the PCs by using the Address Reservation feature at the bottom of the LAN IP setup. Use the Add button, enter the IP addr you want to give to PC1 and then enter the MAC address of the Ethernet adaptor (NIC) in PC1. You find the NIC MAC addrs by using the command ipconfig/all on each PC in turn.
Repeat this address reservation for each required PC (assigning a different IP addr to each PC of course).
Horses for courses; use whatever method that appeals or gives the least work, etc.
That's IP address reservation handled. On now to port-forwarding.