Happy Home
Posted on 8th January 2008
There's a question that has crossed my mind on occasion, but I've never been able to find an answer. Even Wikipedia draws a blank. Someone out there must have a story, although in all likelihood verifying whether it's the right one is another matter. The question is actually in two parts, and while the first might be possible to answer, the second is probably lost in midsts of time.
Why was 127.0.0.1 chosen as the IP address for localhost, and who chose it?
Comments
It's the bits, right?
I've no idea, but thinking about it logically: 127.X.X.X is a loopback address of some kind (with 127.0.0.1 being the first.) In binary this is: 01111111 00000000 00000000 00000000 to 01111111 11111111 11111111 11111111 Making it very easy to match (you only have to check the first byte, and it's all ones) So why wasn't it 11111111 00000000 00000000 00000000 to 11111111 00000000 00000000 00000000 Because 255 is broadcast.Posted by Mark Fowler on Tuesday, 8th January 2008
Who and when...
IANA's assignment list indicates it was reserved in September 1981. A little digging finds RFC 790, "Assigned Numbers", which indicates that Jon Postel reserved the 127 block for IANA then. Unfortunately it's not mentioned in the immediately preceding edition of the Internet Meetings notes, so its precise rationale appears to be undocumented. That said, by 1981 a large amount of the old Class A network blocks had been allocated, and I suspect that Postel picked the 127.*.*.* range as it was the last full four-octet block in that network class (defined in RFC 791, "DARPA Internet Program Protocol Specification", which came out at the same time). This is probably something it's worth asking Vint Cerf.Posted by Earle Martin on Wednesday, 9th January 2008
Thanks
Thanks guys, and thanks Earle for the links.Posted by Barbie on Wednesday, 9th January 2008
