The is a string of hexadecimal digits. IN ISDN 150862028003217 sh. It is encoded as one or two s, i.e., count followed by characters. A host connected to the ISDN may be able to use both the X25 and ISDN addresses, with the local prefix added. The RT resource record provides a route-through binding for hosts that do not have their own direct wide area network addresses.
Smaller numbers indicate more preferred routes.
The format of the RT RR is class insensitive. RT records cause type X25, ISDN, and A additional section processing for . IN RT 2 Relay. IN RT 90 Relay. If it is itself in the set of RT records, it discards any RTs with preferences higher or equal to its own.