The future of military robotics?

May 27, 2008 8:42 AM

Why is the only .arpa website about unicycles?
posted by East Manitoba Regional Junior Kabaddi Champion '94 to technology (9 comments total)

It be part of the tubes architecture.
AKA DNS Reverse Mapping...
posted by iamabot at 8:53 AM on May 27

On 2 seconds after preview, you are savvy enough to use site specific google searches, I can assume I've just been geektrolled.
posted by iamabot at 8:54 AM on May 27

Not trolling.

http://45.135.66.195.in-addr.arpa doesn't work, and http://foo.135.66.195.in-addr.arpa doesn't work. How did this guy get http://unicyclist.135.66.195.in-addr.arpa to work, and why does Google pick it up, and why are there no other sites in the list? Could I do it with my site?
posted by East Manitoba Regional Junior Kabaddi Champion '94 at 9:01 AM on May 27

The zone in-addr.arpa is supposed to be for "reverse" DNS; that is, you have an IP address and you want to look up the name. For example:

$ dig metafilter.com a
...
metafilter.com. 47491 IN A 74.53.68.130
...

There's an A record for metafilter.com that tells us its IP address is 74.53.68.130. Now, flip the IP around and add on ".in-addr.arpa":

$ dig 130.68.53.74.in-addr.arpa ptr
...
130.68.53.74.in-addr.arpa. 86400 IN PTR 82.44.354a.static.theplanet.com.
...

This PTR record (PTR is for reverse DNS) tells us that the name of the IP address is that static.theplanet.com address there. If the admins contacted theplanet.com they could have it changed to metafilter.com, but it doesn't really matter what the reverse DNS is, since nobody really uses reverse DNS on a web server's IP address.

Usually reverse DNS is all anyone uses .arpa zones for, but there's no reason you couldn't put an A record in there. If theplanet.com wanted to, they could assign iamawesome.68.53.74.in-addr.arpa to any IP address they want. The trouble is that to control a zone like that, you need to have a decent-sized block of IP addresses allocated to you, usually at least 256. If 10.1.1.0 through 10.1.1.255 were assigned to you, your ISP would delegate control of the zone "1.1.255.in-addr.arpa" to your DNS servers, and you could put whatever weird stuff in there you wanted.
posted by pocams at 9:20 AM on May 27

For whatever reason, they have put an A record for unicyclist into the zone for their 195.66.135.0/24 subnet.

If you actually have control over your server's reverse DNS zone or can finagle it with your hosting provider I suppose you could actually put an A record in there and have it work.
posted by douglaswth at 9:22 AM on May 27

For whatever reason...

I'm guessing the reason is just for the hell of it.

Interesting question about the dark corners of the internet =)
posted by qxntpqbbbqxl at 9:29 AM on May 27

Whether you can do this with your site depends on how much control you have over the Web server. Can you set up a virtual host so it will accept connections for etc.10.10.10.in-addr.arpa, or are you hosting it on your own IP? If so and if you want this badly, MeMail me and I may be able to arrange it. Caveat: it's pretty stupid, and your URL will be almost as hard to remember as your IP address itself.
posted by pocams at 9:30 AM on May 27

FWIW, some ISPs will "delegate" reverse DNS for subnets as small as /29. (SBCIS used to do this, and may still) They use CNAME to add an extra level of indirection that then is delegated to your name server.

Say you have 172.16.0.0/29. In each of 1.0.16.172.in-addr.arpa - 6.0.16-172.in-addr.arpa they use CNAME to make other DNS servers look for 1.0.0.16.172.in-addr.arpa - 6.0.0.in-addr.arpa. They delegate 0.0.16.172.in-addr.arpa to you. You control your own reverse. (and can put A records in there if you so desire) Happiness ensues.

RFC 2317 provides the basic idea, although differs from SBCIS' implementation in minor detail.
posted by wierdo at 10:18 AM on May 27

http://www.iana.org/domains/arpa/
posted by hal_c_on at 10:39 AM on May 27