[ih] The classful <net>.<host> IPv4 address format

[Jack Haverty]

Probably confusion between decimal and octal.  Octal 12 = decimal 10.  
At that time, the technical world hadn't even agreed on how many bits 
were in a byte, or whether decimal should be replaced by octal or 
hexadecimal.  Or if ASCII was good enough for text encoding.   Or how 
many bits were in a computer word.

The PDP-10 I was using at BBN was (if memory serves...) 10.1.0.5 (not 
10.0.05 as I misremembered).   Arpanet (10), Host 1, IMP 5. Easy to 
remember as dotted quad.  Almost impossible to remember as decimal.   
The TIU we used had a cheat sheet listing the decimal addresses for the 
hosts we were using.

Jack

On 9/14/25 09:40, Barbara Denny via Internet-history wrote:
>   I always thought the ARPAnet was number 10.  On page 1 in this document, the example says 12. Am I missing something? I haven't read the entire document.
> barbara
>      On Sunday, September 14, 2025 at 05:57:16 AM PDT, Craig Partridge via Internet-history<internet-history at elists.isoc.org> wrote:
>   
>   IEN 21 (TCP v. 3) specifies a network.host.port format, which I suspect is
> the origin of the net.host form.
>
> https://www.rfc-editor.org/ien/ien21.pdf
>
> Craig
>
> On Sun, Sep 14, 2025 at 6:21 AM Michael Kjörling via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
>> Every once in a while I see people being surprised that IPv4 addresses
>> can be expressed in formats other than dotted-decimal-quad; more
>> specifically, in classful-style <net>.<host> (where net and host can
>> add up to less than four octets) or even single-large-integer format.
>>
>> I am _almost_ certain that I have seen an early IP or TCP RFC which
>> actually describes this representation, but have been unable to locate
>> that.
>>
>> Can anyone point me at an authoritative source where the
>> dotted-not-quad textual IPv4 address representation format is defined
>> or at least described? Thanks!
>>
>> --
>> Michael Kjörling
>> 🔗https://michael.kjorling.se
> mailing lists.

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