possible new project: better realm determination heuristics -- any takers?

Mark Phalan Mark.Phalan at Sun.COM
Tue Apr 8 02:14:33 EDT 2008

On 7 Apr 2008, at 20:54, Ken Raeburn wrote:
> One area we're looking to improve our package is in configuration
> requirements -- minimizing the need to manually set up the config file
> on client hosts -- and realm determination, both of server hosts and
> especially of the local host as a client, is a particular case of
> this.  Is anyone interested in making some improvements in this area?
> Currently, we look for default_realm in the config file, and if that
> doesn't work, and the compile-time and run-time configurations allow,
> we try looking up some "_kerberos" TXT records in DNS, and then give
> up. But our code for determining the realm of a server host does other
> checks that we don't do for the local realm, like checking the current
> hostname and parent domains in the domain_realm mapping table;
> aligning the two sets of heuristics, to the degree that it makes
> sense, would also be helpful.
> There are probably other fairly cheap heuristics that could be
> implemented as well, for both servers and default realm
> determination.  For example, guess that the hostname itself, or the
> parent domain, is also the realm name, and see if we can figure out
> where the KDCs are; if we can't, retry with the next domain up towards
> the root.

I basically implemented this heuristic for our (Sun's) code.
If you're interested I can make a patch for MIT 1.6.3 ?

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)
	realm = NULL;

    return (realm);

This was suggested by Nico back in Dec 2006.


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