A client section can be specified based on wildcards (since V1.7). Please use this with care. Recommendation is to not use client-id based specifications (UseClientID=0) and also to make sure that no interference with IPOOLs is possible, because the DHCP Server is not able to check this. This is how it works:

A client section can be defined based on wildcards like this:

[00-01-02-03-04-??]
IPADDR=192.168.17.%m5

What happens is that if a client that matches the above wildcard asks for an IP address, that the IP address assigned is automatically composed by using mac address byte 5 (%m5). The resulting mac address for client [00-01-02-03-04-6A] will be 192.168.17.106. (6A hex is 106 dec).
Mac address byte 0 through 5 are accessed accordingly with %m0 through %m5. The wildcard match algorithm searches in the following order and takes the first matching entry:

[00-01-02-03-04-6A]
[00-01-02-03-04-??]
[00-01-02-03-??-??]
[00-01-02-??-??-??]
[00-01-??-??-??-??]
[00-??-??-??-??-??]
[??-??-??-??-??-??]

In addition to the %m0 through %m5, since V2.3.1 there are further macros available. These are %ip0 through %ip3. They allow to access the IP address of the IPBIND_n address used by the current DHCP request. If IPBIND_1 is defined as IPBIND_1=192.168.5.1, then the macros are extended to: %ip0=192, %ip1=168, %ip2=5 and %ip3=1.