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I just noticed today that domain foo.bar resolves to 127.0.53.53 (http://foo.bar, http://whois.domaintools.com/foo.bar)

In my case this ends up on the localhost Apache, but I wonder why the registrant did not simply chose to point to 127.0.0.1? Is there any specific reason?

Ozh
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1 Answers1

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127.0.53.53 is a special IP addresses that is used by ICANN to prevent DNS name collisions with the new gTLDs.

In your case the .bar gTLD was delegated in February. So the 127.0.53.53 is a big hint for people using .bar in their internal setups that the .bar domain name will be used in the global DNS very soon.

If you look closer at the foo.bar record you see more information:

$ dig foo.bar A +short
127.0.53.53
$ dig foo.bar TXT +short
"Your DNS configuration needs immediate attention see https://icann.org/namecollision"
$ dig foo.bar MX +short
10 your-dns-needs-immediate-attention.bar.
$ dig foo.bar SRV +short
10 10 0 your-dns-needs-immediate-attention.bar.
SUB0DH
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Sebastian Wiesinger
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    Who is "we"? 127.0.53.53 was chosen because it makes searching for this issue simple. Also there is no functional difference between 127.0.0.1 and 127.0.53.53. – Sebastian Wiesinger Apr 05 '15 at 14:21
  • Sebastian, TCP/IP stacks won't respond to requests destined for 127.0.53.53, but they will respond to requests destined for 127.0.0.1. That is a big difference. @jrmgx Yes, use a local DNS server like dnsmasq and point your local DNS to 127.0.0.1 and you can resolve *.bar (or anything, really) to whatever you want, including 127.0.0.1. – Greg Schmit Dec 28 '16 at 23:18
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    @GregSchmit ping 127.0.53.53 ;) Systems respond to everything under 127/8. – Sebastian Wiesinger Jan 04 '17 at 22:07
  • @Sebastian Silly Windows stacks will assign it to localhost (wrongly), but Unix systems (e.g., OS X or FreeBSD) will do the Right Thing. ;) https://drive.google.com/open?id=0B8A0lXQwAyCiSjZTRFdmNXVNU0U – Greg Schmit Jan 04 '17 at 22:16
  • @Sebastian And I hope you meant *within* 127.0.0.0/8, not below it. There is an argument that the whole block should loopback from the wording of RFC3330, but most stacks don't (and IMO, shouldn't; think of all the stuff we can do with those IP addresses!). – Greg Schmit Jan 04 '17 at 22:21
  • I meant every IP in 127/8. At least my Windows 10 responds to any address in 127/8. – Sebastian Wiesinger Jan 04 '17 at 22:24
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    Linux also responds on all IPs in 127/8 – Habbie Sep 21 '17 at 07:18