IPv4 address length technical design

Wed Oct 3 21:30:53 UTC 2012

Remember that at the time, IP was designed to be classful so having four 8 bit bytes was real convenient to look only at the bytes in the host portion of the address.  Class A meant three significant bytes, Class B had two significant bytes, and Class C had three significant bytes as far as the host portion of the address.  If we are looking for matches in a routing table it is much easier to search for an entire matching byte than to do it bitwise.  Even though systems had varying byte lengths, 8 was still the most common because it was the easiest to map extended ASCII into.

Now we could discuss whether there should have been more bytes but at the time no one had really envisioned the public deployment of this at the scales we see today.  Same reason IBM and Microsoft had barriers like 640k of RAM, no one just ever thought you would need more than that.

Steven Naslund

-----Original Message-----
From: Seth Mos [mailto:seth.mos at dds.nl] 
Sent: Wednesday, October 03, 2012 11:53 AM
To: nanog at nanog.org
Subject: Re: IPv4 address length technical design

Op 3-10-2012 18:33, Kevin Broderick schreef:
> I'll add that in the mid-90's, in a University Of Washington lecture 
> hall, Vint Cerf expressed some regret over going with 32 bits.  
> Chuckle worthy and at the time, and a fond memory
> - K

"Pick a number between this and that." It's the 80's and you can still count the computers in the world. :)

It is/was a "experiment" and you have the choice between a really large and a larger number. Humans are not too good in comparing really large numbers. If it was ever decided to use a smaller value, for the size of the experiment it might have went quite different. The "safe" (larger) choice ended up bringing more pain.

As a time honored ritual, the temporary solution becomes the production solution.

Oops... And that was not quite what Mr Cerf meant to do.

Regards,

Seth