🚀 go-pugleaf

>Please excuse the cross-posting to TCP/IP, BIGLAN, and IBMNETS.
>
>We are in the thinking/planning stage for our campus network.
>We are considering creating different classes of subnets
>analogous to the classes of internet addresses.  In his TCP/IP
>book Comer says that this is possible but that most sites prefer
>fixed subnet masks.
>
>Are there sites with subnet classes?  If so, what has your
>experience been?

The biggest problem with variable sized subnets is finding software
to support it!  Here at Michigan State University, we are running in
a class B subnet of net 35, which is assigned to Merit (really 8 * class B,
but we're only using one so far).  And University of Michigan uses a
number of class C subnets of net 35.  The only implementation of subnetting
that I have seen that does subnet masks properly is Merit's own.

It's not that it is technically difficult to provide minimal support for
varying sizes of subnets - all you need is one net mask per routing table
entry.  But there's little market pressure to solve this problem because
few sites are making any real use of subnets.  If they are, they have a
few class C subnets of their class B net, or some such.  And one net mask
per interface (per host?) suffices for this use.

The next problem, after allowing subnet routes to be defined properly in a
host or router, is to develop or extend a routing protocol to deal with
subnet routing within a "local" context.  This isn't as trivial as the
first problem, and I suspect is why variable subnets aren't being addressed.

So in answer to your question, I'd recommend sticking with one size for
your subnets for now, and in the meantime those of us who are stuck with
this configuration can prod the vendors for some support.

Doug Nelson
Network Software Manager
Michigan State University