|
In an effort
to conserve ip addresses as well as to make our routing more efficient,
we are now using different subnet masks, and in many cases, a different
gateway address for *new* networks. (Note that these masks are often
referred to as variable length subnet masks or VLSM.) Established
networks will continue to use whatever mask and addressing that
they are presently using.
Up
until this time, we used a subnet mask of 255.255.255.0 on all of
our networks, and (in most cases) a gateway address of 128.151.x.250.
For the NCS
test network in Towne, for example, the network address is 128.151.77.0,
the subnet mask is 255.255.255.0 and the gateway is 128.151.77.250.
In this scheme,
254 addresses could be used on our network (128.151.77.1 through
128.151.77.254). This works fine on larger networks, but it is a
waste of address space for smaller networks - as the addresses can
not be used elsewhere.
The subnet
mask is used simply to divide an ip address into network and host
portions. By changing it, we will be creating more networks, but
with smaller numbers of hosts in each than previously.
Here are masks
that we will most likely use and the number of networks and hosts
possible for each mask:
Here is an example
of how the ip addresses are assigned in this new scheme. A new network
has been installed for a small department on campus. We have allowed
for 30 possible addresses on their network. These are the addresses
assigned to them:
default gateway (or router address): |
128.151.191.62 |
broadcast address: |
128.151.191.63 |
subnet mask: |
255.255.255.224 |
possible host addresses on this net: |
128.151.191.33 through 128.151.191.60 |
Another example
- a new network has been installed on one of our offsite locations.
We have allowed for 62 possible addresses on their network:
default gateway (or router address): |
128.151.125.126 |
broadcast address: |
128.151.125.127 |
subnet mask |
255.255.255.192 |
possible host addresses on this net: |
128.151.125.65 through 128.151.125.124 |
|
