Slashdot Mirror
Mirror Listings Though TXT DNS Records?
mackman asks: "I was wondering if anyone has ever though about using their DNS servers to provide mirror information? A specially formated TXT-record could easily provide a DNS-cache-friendly mirror listing. A TXT-record would just need a list of servers and paths, or perhaps a more complicated mapping for servers which only mirror a subset of the original site. This would allow for much more flexibility than a basic round-robin A-record scheme. For example, instead of pounding the Red Hat web server to get a mirror listing (or relying on Slashdot posts for that matter), why not do a 'dig -t txt mirrors.redhat.com'? Of course we could build this into download managers like wget."
Then what are these mx records being used to relay mail. That's not exactly application neutral. You can place any random text you want to in a dns record. If you do a host -a you will occasionally come across people who have thrown completely random shit into their dns record. The A record is what is used to resolve a hostname to an ip address. Here is a list of other record types from nslookup(1):
A the host's Internet address.
CNAME the canonical name for an alias.
HINFO the host CPU and operating system type.
MX the mail exchanger.
NS the name server for the named zone.
SOA the domain's ``start-of-authority'' information.
TXT the text information.
WKS the supported well-known services.
Other types (ANY, AXFR, MB, MD, MF, NULL) are described in the RFC-1035 document.
I seem to recall something about jabber using a dns record similar to mx. A quick google search comes up with this page that claims both ldap and jabber use srv records and that jabber formerly used the mx record.
So yeah, dns, more than just ip addresses and hostnames.
DNS is designed to be an extensible, flexible, distributed, and massively scaleable lookup database. It is quite suited to what you propose, and has certainly been used for much lamer ideas already.
I wouldn't use TXT records, though. SRV records might be more appropriate, but people are apparently using SRV for LDAP nowadays so you're probably better off just defining a new type. Use the procedure laid out in the RFCs for designating a new type of "experimental" DNS record, so that everyone will be compatible with you (well, everyone that follows the RFCs, anyway, which might leave out MS and DJB) or figure out how to use one of the obsolete record types.
You can look at some of the other types of records in RFCs 1035, 1183, 1706, 1886, 2672, 2782, and 2874. Most of the important ones (well, other than IPv6 stuff) are in RFC1035.
Incidentally, you're going to get dozens (if not hundreds) of posts here that will say "You shouldn't do that with DNS!". Pretty much any question you ask around here that even mentions DNS will get the same result, so just ignore them. I think these people are a lot more interested in shooting down ideas than in actually testing them, which is the only real way to find out if they will work.