Is there a reason "localhost" resolves to SERVER_ADDR "::1" under Apache?

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Level 2

185 points

Is there a reason "localhost" resolves to SERVER_ADDR "::1" under Apache?

I don't see any mod_rewrites or such, but PHP reports $ SERVER['SERVERADDR'] as "::1" when using "http://localhost" to access my local Apache server.

"http://127.0.0.1" works as expected.

Is this an artifact of all Apache servers on all hosts when referenced as "localhost"?

G5 Dual-2GHz; eMac G4-1GHz; Pismo G3; iMac (Intel); 2 MBPs, tv, ..., Mac OS X (10.5.4)

Posted on Dec 28, 2009 10:23 PM

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Answer 1

BobHarris

Level 9

56,951 points

Dec 29, 2009 8:38 AM in response to Jon Milan

::1 is most likely an IPv6 localhost address.
<http://en.wikipedia.org/wiki/Localhost>

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Answer 2

Camelot

Level 9

58,617 points

Dec 29, 2009 10:37 AM in response to Jon Milan

::1 is, indeed, the IPv6 equivalent of IPv4's 127.0.0.1, i.e. localhost

If your machine is configured to use IPv6 then the resolver will return IPv6 addresses by default, so that's why 'localhost' resolves to ::1 and that's what Apache/PHP report.

If you don't like that, turn off IPv6 in System Preferences -> Network. If your machine isn't running IPv6 then localhost will resolve to the IPv4 address you're familiar with.

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Answer 3

Jon Milan Author

Level 2

185 points

Dec 29, 2009 10:42 AM in response to BobHarris

Bob, I'd suspected this, but hadn't seen it explained. Thanks!

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