The RT RRs require the following RDATA fields:

• <preference> (a 16 bit integer representing the preference of the route, smaller numbers indicate more preferred routes)
• <intermediate-host> (the domain name of a host which will serve as an intermediate in reaching the host specified by <owner>, the DNS RRs associated with <intermediate-host> are expected to include at least one A, X25, or ISDN record)

The format of the RT RR is class insensitive. RT records cause type X25, ISDN, and A additional section processing for <intermediate-host>.

More information on the RT record is documented with RFC 1183.