This is not RESTful. A way to implement this could be to introduce scoping to the index operation, ie: GET /dhcp would return all records, while GET /dhcp?ip=192.168.42.1,192.168.42.3 would only return records with the ip addresses included in the list. filtering by mac addresses could be done similarly: GET /dhcp?mac=aa:aa:aa:aa:aa,bb:bb:bb:bb:bb.

Also, in this particular approach we'd be doing search based on the explicit parameters passed in by the user, instead of trying to guess the meaning of supplied data, which is always better.