All negative values for the host address type are reserved for local use. All non-negative values are reserved for officially assigned type fields and interpretations.
The values of the types for the following addresses are chosen to match the defined address family constants in the Berkeley Standard Distributions of Unix. They can be found in <sys/socket.h> with symbolic names AF_xxx (where xxx is an abbreviation of the address family name).
Internet addresses are 32-bit (4-octet) quantities, encoded in MSB order. The type of internet addresses is two (2).
CHAOSnet addresses are 16-bit (2-octet) quantities, encoded in MSB order. The type of CHAOSnet addresses is five (5).
ISO addresses are variable-length. The type of ISO addresses is seven (7).
XNS addresses are 48-bit (6-octet) quantities, encoded in MSB order. The type of XNS addresses is six (6).
AppleTalk DDP addresses consist of an 8-bit node number and a 16- bit network number. The first octet of the address is the node number; the remaining two octets encode the network number in MSB order. The type of AppleTalk DDP addresses is sixteen (16).
DECnet Phase IV addresses are 16-bit addresses, encoded in LSB order. The type of DECnet Phase IV addresses is twelve (12).