[ih] History of 127/8 as localhost/loopback addresses?

[Carsten Bormann]

On 2021-01-02, at 16:52, Carsten Bormann via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> 4.2BSD

Found it (below).
Note that, in March 1982, it said “non-standard” about the address 127.0.0.1, and maybe a bit ruefully “An approved network address should be reserved for this interface”.

That is also my recollection: 

The squatting on 127/8 for this was common usage, “harmless” at the time as that range had not been allocated, but not actually standardized anywhere (but soon immutable by having been encoded in hundreds of applications).

If it had been the subject of standardization discussion, a class C address might very well have been chosen after giving it a tiny amount of additional thought — but then RFC 844 as late as February 1983 gave a survey that meant to address how many hosts supported class C already, so maybe class A was still the logical thing to choose in 1982; class C seems to have been introduced between January 1981 (RFC 776) and September 1981 (RFC 790).

Note that BSD also had 0.0.0.0 to talk to yourself; “telnet 0 22” (*) still connects on my current laptop...

Grüße, Carsten

(*) branching over to the dotted quad discussion :-)

> UNIX Programmer’s Manual 
> 
> LO (4) 
> 
> NAME 
> 
> lo — software loopback network interface 
> 
> SYNOPSIS 
> 
> pseudo-device loop 
> 
> DESCRIPTION 
> 
> The loop interface is a software loopback mechanism which may be used for performance 
> analysis, software testing, and/or local communication. By default, the loopback interface is 
> accessible at address 127.0.0.1 (non-standard); this address may be changed with the SIOCSI- 
> FADDR ioctl. 
> 
> DIAGNOSTICS 
> 
> lo%d: can’t handle af%d. The interface was handed a message with addresses formatted in an 
> unsuitable address family; the packet was dropped. 
> 
> SEE ALSO 
> 
> intro (4N), inet(4F) 
> 
> BUGS 
> 
> It should handle all address and protocol families. An approved network address should be 
> reserved for this interface. 
> 
> 
> 4th Berkeley Distribution 
> 
> 
> 26 March 1982