IPv4 address length technical design
bjorn at leffler.org
Thu Oct 4 15:39:46 UTC 2012
On Wed, Oct 3, 2012 at 12:13 PM, Chris Campbell <chris at ctcampbell.com> wrote:
> Is anyone aware of any historical documentation relating to the choice of 32 bits for an IPv4 address?
I've heard Vint Cerf say this himself, but here's a written reference
for you. They had just finished building arpanet, which was expensive
to build. Hence why they estimated two networks per country.
When developing IPv4, Cerf said that he and Bob Kahn “estimated that
there might be two national-scale packet networks per country and
perhaps 128 countries able to build them, so 8 bits sufficed for 256
network identifiers. Twenty-four bits allowed for up to 16 million
hosts. At that time, hosts were big, expensive time-sharing systems,
so 16 million seemed like a lot. We did consider variable length and
128-bit addressing in 1977 but decided that this would be too much
overhead for the relatively low-speed lines (50 kilobits per second).
I thought this was still an experiment and that if it worked we would
then design a production version.
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