Subnetting under SunOS 4.0?

[Frank W. Peters]

Hello,

We have a large, unsubnetted, class B network (130.18) on our campus.
Though this network is unsubnetted addresses are assigned in a subnetted
fashion (that is, each building has its own 'subnet number' although no
subnet mask is actually in use).

In one of the buildings we are currently attempting to attach we have
several Sun 4 servers running 4.0 (one is running 4.0.1).  To isolate NFS
traffic each of these servers has two ethernet cards.  One card attaches
to the campus network while the other attaches to the server's diskless
clients.  Each of the client networks has its own 'subnet number' of the
class B network.  In order to allow the servers to have portions of the
same network on two different interfaces it seems that some degree of
subnetting is necessary.

Now we come to the question of how, exactly, to configure these servers.

Our first pass was to subnet the test server (in a class C manner).  We
set the broadcast address to 130.18.255.255 so that the unsubnetted hosts
would be able to converse with the servers.  When we attempt to boot under
this configuration we get the error:

     Unable to send Broadcast:  Network is unreachable

and ypbind hangs because it cannot reach a ypserv (this all ocurring on
the ypserver machine itself).  When we set the broadcast to the subnetted
address (ie 130.18.64.255) the machine boots.

So, in short, why does:

ifconfig ie1 $hostname up -trailers netmask 255.255.255.0 broadcast \
  130.18.64.255

allow the machine to boot (and yp to start) when

ifconfig ie1 $hostname up -trailers netmask 255.255.255.0 broadcast \
  130.18.255.255

doesn't?

==========

Assuming that we can solve the above problem then the following question
becomes relevant.

The above solution still leaves some problems.  Since the servers are
subnetted they still refuse to communicate directly to hosts that are not
on the same subnet.  That is, machine 130.18.64.11 refuses to speak to
130.18.96.64 because that machine is not on the same subnet (even though
it is directly reachable).  What would actually be the ideal solution is
for the servers to be subnetted on the client side and unsubnetted on the
server side (this is perfectly legal under the RFCs, its just a matter of
logistics).

I note in the documentation that a subnet mask is assigned on each
interface.  I have been given to believe that, under 4.0{.1} it is
possible to subnet one interface and leave the other unsubnetted.

What I envision is the following ifconfig for the interface on the
unsubnetted backbone:

ifconfig ie1 $hostname netmask 255.255.0.0 up -trailers

and the following on the client side:

ifconfig ie1 $hostname netmask 255.255.255.0 up -trailers

Will the above entries accomplish the desired goal (allowing the backbone
side to be unsubnetted while subnetting the client side)?  If not, do you
have any pointers to the correct method to accomplish this?

	Frank Peters

Systems Programmer                 |   Mississippi State University
Phone:    (601) 325-2942           |   Computing Center and Services
Internet:  peters at CC.MsState.Edu   |   Post Office Drawer CC
BITNET:    PETERS at MSSTATE.BITNET   |   Mississippi State, MS.  39759