Null realms and servers

Derek Atkins warlord at MIT.EDU
Wed Dec 20 09:51:14 EST 2006

Nicolas Williams <Nicolas.Williams at> writes:

>> How do you determine the base domain for a realm hierarchy?
>> E.g. what kind of algorithm do you use to decide whether
>> w.x.y.z maps to Y.Z or X.Y.Z?  For example, how would you
>> handle  Or even
>> Obviously you wouldn't want this to map to domain AC.UK.
> The algorithm is:
>     domain = fqdn;
>     while (domain.label_count > 2) {
> 	domain = pop_label(domain);
> 	realm = domain2realm(domain); /* for ASCII: toupper() */
> 	if (lookup_kdcs(realm) > 0)
> 	    break;
> 	realm = NULL;
>     }
>     return (realm);
> This does depend on having FQDNs, which means we still have to solve the
> secure hostname canonicalization problem.  (More on that in a separate
> thread, some other time.)

Ahh, there's the "lookup_kdcs()" step.  That makes sense, and
answers the question.  At each step in the FQDN you perform an
active check to see if there's a realm at that level.

> Nico


       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL:    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available

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