Date: Tue, 24 Feb 2009 15:21:38 -0600
From: John David Stone 
To: Janet Davis 
Subject: Re: MathLAN subnet

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> I thought the MathLAN had its own IP subnet within Grinnell's class B
> address block, but ifconfig on ladd tells me this:
>
> inet addr:132.161.196.148 Bcast:132.161.255.255 Mask:255.255.0.0
>
> Am I wrong about the subnetting? Could you clarify?

In 1987, when MathLAN was set up, ITS allocated the range from
132.161.30.0 to 132.161.39.255 to us, but did not designate us as a subnet.
At that time, all the machines on campus used the class B netmask. There
were routers to connect different Ethernet segments, but they didn't act as
filters.

When the dorms were wired, they received their own subnet, and
MathLAN probably should have started using a different netmask at that
time, but I never got any official word from ITS about what the netmask
should be (I would guess that it should have been 255.255.128.0, but I
never got this surmise confirmed) and never encountered any problem with
using 255.255.0.0, so it never got changed.

As part of phase II, MathLAN got its own "virtual subnet," and most
of our workstations received new IP addresses from the class C blocks
132.161.196 (for CS) and 132.161.197 (for Math). The remaining
workstations and servers that have addresses from our former range probably
won't change until they are replaced, however.

The class B netmask still doesn't seem to be causing any problems,
but David Ellis now wants me to switch over to 255.255.254.0 (with
corresponding changes to the broadcast address), and making this change on
all the 132.161.196.* and 132.161.197.* machines is on my to-do list for
summer.

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