[ih] Dotted decimal notation

[Brian E Carpenter]

Thanks for the various replies. I wasn't there, but clearly some magic
happened between the 8-bit network numbers in RFC776 (January 1981) and
the emergence of Class A, B, C addressing in RFC790 (September 1981),
and that called for some new notation such as dotted decimal.

That magic is not well documented in the RFC series, but in IEN175,
reporting on a January 1981 meeting, we find that
      "Vint Cerf led a further discussion on addressing.  The main focus
      was on the tradeoff between a flat address space and a
      hierarchical one...
      Vint suggests that we have both in one!  Let an address be
      composed of two parts: a hierarchical address (called an address)
      and a flat address (called an identifier)."

I guess that became Class A, B, C by September, via IEN177, but it also
accurately describes IPv6 addressing.

Regards
   Brian Carpenter

On 29-Dec-20 10:54, Jack Haverty via Internet-history wrote:
> IIRC, this convention was created over time by a coalescence of "rough
> consensus and running code" as the early user programs (Telnet and FTP)
> were being rewritten to use TCP instead of NCP, so it would have been
> during the late 70s.   On the ARPANET, e.g., when a particular Telnet,
> you would type "O <host>/<imp>", e.g., 1/6 to connect to MIT-DMS, host 1
> on IMP 6, or "O 70" which was the equivalent.   Something new was needed
> for specifying 32-bit IP addresses.
> 
> Dotted quad was one early approach, where the 4 numbers could be either
> octal, if they had a leading zero, and otherwise decimal. 
> A leading 0 indicated that the number was octal - also a common
> convention in programming languages at the time.
> 
> The "dotted decimal" convention evolved from the "dotted quad", with the
> difference being that the numbers in the "...decimal" form were of
> course always decimal, regardless of the presence of a leading zero.  
> 
> I believe all of these forms were created as various people wrote user
> programs.  The notation is really a design decision of the user
> interface, converting typed IP addresses into the appropriate 32-bit
> fields for the underlying TCP code.
> 
> Some people liked decimal numbers, others liked octal. 
> 
> One particularly irritating choice was pure decimal, i.e., a 32-bit
> number represented in decimal (no dotted quad).   The early SRI TIU
> (terminal concentrator) required the user to input decimal numbers,
> which were annoyingly difficult to calculate.    E.g., 10.0.0.5, easily
> recognized as Host 0 on ARPANET IMP 5, had to be typed in its 32-bit
> decimal format when specifying what remote computer the user wanted to
> access.  It was difficult to do such calculations in your head; I
> remember pulling out a calculator to create the appropriate many-digit
> decimal number.
> 
> Eventually the "dotted quad" notation reached rough consensus and many
> host implementations of user apps (Telnet, FTP) permitted that form of
> specifying a target host.
> 
> The "dotted decimal" convention eventually superceded the "dotted quad"
> notation because the quad form was often confusing. 
> 
> E.g., "ISIF in dotted decimal is 010.002.000.052, or 10.2.0.52", where
> leading zeroes are ignored.  But in dotted quad,
> 010.002.000.052 and 10.2.0.52 would not be equivalent.  010 would be
> network 8 rather than 10, and 052 would be 42 instead of 52.
> 
> I don't remember who first produced dotted decimal though.   I think
> you'd have to look at the applications programs of the time (FTP,
> Telnet) to see what each used for its UI.
> 
> /Jack
> 
> 
> On 12/28/20 12:55 PM, Brian E Carpenter via Internet-history wrote:
>> Can anyone recall when and by whom the dotted decimal notation for IPv4
>> addresses was invented? This text first appeared in RFC820 (January 1983):
>>
>>    One commonly used notation for internet host addresses divides the
>>    32-bit address into four 8-bit fields and specifies the value of each
>>    field as a decimal number with the fields separated by periods.  This
>>    is called the "dotted decimal" notation.  For example, the internet
>>    address of ISIF in dotted decimal is 010.002.000.052, or 10.2.0.52.
>>
>> The leading zeroes are not considered valid these days.
>>
>> Thanks 
>>    Brian Carpenter
>