Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!mips!apple!escher From: escher@Apple.COM (Michael Crawford) Newsgroups: comp.sys.mac Subject: Re: NCSA Telnet questions Keywords: telnet Message-ID: <7692@goofy.Apple.COM> Date: 13 Apr 90 19:04:41 GMT References: <793@thebeach.UUCP> <7644@goofy.Apple.COM> Organization: Apple Computer Inc., Cupertino, CA Lines: 50 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.