'Compare an rdata with another rdata of the same rdtype and
rdclass.  Return < 0 if self < other in the DNSSEC ordering,
0 if self == other, and > 0 if self > other.'

def _cmp(self, other):

    our = self.to_digestable(dns.name.root)
    their = other.to_digestable(dns.name.root)
    if (our == their):
        return 0
    if (our > their):
        return 1
    return (-1)
