The reservation of IP addresses usually serves the purpose of excluding IP addresses or address ranges from the IP pool. Mostly, because those IP addresses are already known to be used somewhere in the network and are not to be reused or controlled by DHCP. There are two ways on how to reserve IP addresses.

1. Define the IP pool with defined excludes

The easiest way is to define the IP pool in a way such that the IP addresses you don’t want to be served by means of DHCP are not even part of the pool. Here is an example:

[Settings]
IPPOOL_1=123.45.56.78-90,92,94,100-110

This defines an IP Pool from 123.45.56.78 until 123.45.56.110 excluding (reserving) the following IP addresses:123.45.56.91, .93, .95, .96, .97, .98, .99. The excluded IP addresses will not be served by means of DHCP and can therefore be used in the network for static assignments.

2. Add static client entries to the INI file

Another way is to simply add client entries to the INI file. The DHCP server will not serve IP addresses that are already occupied in any client section in the entire INI file. Assuming there is a device on your network with the static IP address 123.45.56.101. The corresponding client entry that you can add to the INI file could look like this:

[IP_123.45.56.101]
IPADDR=123.45.56.101

Please note the IP_123.45.56.101 heading. Here you would normally expect the MAC address of the device. If you know it, then of course you can use that as well. If you don’t know it then it doesn’t really matter what section heading the client section has, as long as it is unique throughout the INI file. This can easily be achieved as shown here with IP_123.45.56.101. With that client section in the INI file, the address 123.45.56.101 will no longer be served by the DHCP server (it is reserved).