🚀 go-pugleaf

In article <7644@goofy.Apple.COM> escher@Apple.COM I write:
>
>The subnet mask tells the host what part of the adress to use for
>the net+subnet pair.  Note that you can set it on any bit -- you
>can subnet class C addresses, so you could have two networks with
>127 hosts each.
>

I made a mistake here... apparently the subnet mask must be at
least two bits past the net number.  Thus you may have up to four
subnets of 64 hosts each on a class C net, but not two nets of 127
hosts each.  Or 62 hosts, rather: don't use all 1's for the host
number, that is the broadcast address; all 0's sometimes means the
net itself, and is used as the broadcast address (incorrectly!) by
BSD 4.2 Unix systems.

Note that your broadcast address will be all 1's in the host part
only, and not in the (subnet, host) part.  MacTCP takes care of
this itself, but A/UX has you set it manually.  When I installed
an A/UX router, I was used to the mistaken idea that one would only
set the subnet at a byte boundary, where Apple uses 10 bits for
its host number.  Thus, I was addressing all my broadcasts to host
256 on my subnet.  Fortunately, no one was there to receive them.

Note that it is also important to have a unique address.  Someone
was in a hurry to set up PC-NFS when I was out of the office, so
someone just told him to "Pick a high number.  It's not likely to
be used."  When I got back in there was an urgent message from the
person whose number he had picked and whose net was down, and one
from him saying he could not get PC-NFS installed!

If you have a big site, where it is too slow, or inconvenient to
have a single administrator hand out all the addresses, assign an
administrator for each subnet, and have her hand out the addresses.
If even this is unsatisfactory, have each manager assigned a range
of addresses on the net, to assign to her employees as they need
them.  In any case, set up a quick convenient scheme for people to
get their addresses, so they won't try just guessing one!
-- 
Michael D. Crawford
Oddball Enterprises
606 Modesto Avenue
Santa Cruz, CA 95060
oddball!mike@ucscc.ucsc.edu

Consulting for Apple Computer Inc.
escher@apple.com
Applelink: escher@apple.com@INTERNET#

The opinions expressed here are solely my own.