Integrated DNS and web referral -- How??

[dps...@dpsims.com]

I have noticed that some Domain Registrars seem to offer an integrated
web referral service. For instance, in the registrar's DNS control
panel, you can set a link from a DNS name <foo.bar.com> to a website
subdirectory like <http://cis.boom.org/foo>. Anyone have a clue how
this is done at the level of DNS?? I could imagine that you could
point a DNS name like foo.bar.com to a webserver where a 'referral'
snippet might exist as the index.html referring to http://cis.boom.org/foo
but I am not aware of any public domain programmatic way of doing
this.... Any clues or suggestions??

Thanks,

Dave