There appears to be an undocumented (in src/config-files/krb5.conf.M)
"rdns" setting in the [libdefaults] section of krb5.conf. Confirmed in
branches/krb5-1-8 and trunk.

It would be good to add some documentation about this feature.

Cheers,
Dominic.

-- 
Dominic Hargreaves, Systems Development and Support Team
Computing Services, University of Oxford