I think I understand what you're asking about. You have two types of entities that may share some common information between them (in particular, "What am I connected to?"), but have a lot of fundamental differences (I could imagine the IP-based devices having a field for "IP Address" whereas the Serial-based ones wouldn't).
You may want to do some research on the term "single-table inheritance". This is a technique whereby a single table contains all of the fields for both types of entities. Some of these fields will be common to both types, but some of them will only be applicable to one type or the other. Under STI that's expected; you usually have a field which indicates which "type" of entity the record represents, and the fields that aren't applicable will all be set to NULL.
Alternately, you can do a similar thing with multiple tables. You could have a Hardware table to represent the common data, and then IPHardware and SerialHardware tables to represent the data specific to each type. The latter two tables could then have a Foreign Key reference to the Hardware table to make a reference to their own "common" data. Other tables would typically reference the Hardware table and then drill-down into the "subclass" tables depending on their needs & the type of the Hardware.