[763] in Commercialization & Privatization of the Internet
IETF questions -- Internet growth
daemon@ATHENA.MIT.EDU (Barry Shein)
Wed May 29 18:02:48 1991
Date: Wed, 29 May 91 18:00:09 -0400
From: bzs@world.std.com (Barry Shein)
To: francis%zaphod@gargoyle.uchicago.edu
Cc: emv@ox.com, solensky@animal.clearpoint.com, ietf@venera.isi.edu,
In-Reply-To: francis%zaphod@gargoyle.uchicago.edu's message of Wed, 29 May 91 16:11:40 CDT <9105292111.AA01562@arthur.uchicago.edu>
>Is there any reason, aside from routing table size, to worry too much
>about number assignment? Isn't an IP address 4 bytes, giving
>4,294,967,296 possible addresses?
Well, no, the address space is segmented and there are other
considerations, so it's, hmm:
Class A: 126 (assume 0 and 127 not available)
Class B: 16,384 ((192-128)*256)
Class C: 4,194,304 ((256-192)*256*256)
-----------
4,210,814 NETS
Now, for maximum hosts, this assumes no subnetting where intermittant
255's might be magic (broadcast):
Class A: 2,113,928,964 (126*2^24 - 2*126)
Class B: 1,073,709,056 (16384*2^16 - 2*16384)
Class C: 1,065,353,216 (4194304*256 - 2*4194304)
-------------
4,252,991,236 HOSTS
[Note: The "- 2*netsize" is to account for no all-ones nor all-zeros
host numbers]
What's potentially interesting is how those hosts are distributed
among network classes and how that corresponds to network number
assignment. The big thing that jumps out is that there are "only"
about 4M networks possible.
This is reminiscent of the unix "out of inodes" problem where your
disk can be half empty but you can't create a file if you set things
up unfortunately. If people are going to have networks in small
organizations throughout the world 4M doesn't seem like all that many
to go around.
I'm also curious if anyone can find a flaw in this beyond pointing out
that subnetting potentially reduces it quite a bit. It seems too large
to me, maybe not. I've never seen the calculation carried out and some
authoritative answer popularized, although I am sure many have done it
informally. Also, how many Angstroms to Alpha Centuri? Hey, it's a
rainy day in Boston...
-Barry Shein
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