Subnetting
Guidelines
Introduction
There is always that day when you are called upon to
provide a solution to a network problem. The number
of problems that can occur in a network are numerous
and believe it or not, most of them can be avoided
if the initial design and installation of the
network are done properly.
When I say "done properly" I don't just mean
connecting the correct wires into the wall sockets !
Looking at it from an Administrator's point of view,
I'd say that a "properly done job" is one that has
had a lot of thought put into it to avoid silly
routing problems and solve today's and any future
needs.
This page contains all the information you need to
know in order to design a network that won't suffer
from any of the above problems. I've seen some
network setups which suffered from all the above,
and you would be amazed how frequently I see them at
large companies.
Guidelines
- Plan
for Growth
When creating subnets for your network, answer the
following questions:
-
How many subnets are
needed today?
Calculate the maximum number of subnets required
by rounding up
the maximum number to the nearest power of two.
For example, if an organization needs five
subnets, 2 to the power of 2 or 4 will not
provide enough subnet addressing space, so you
must round up to
2 to the power of 3 = 8 subnets.
-
How many subnets are
needed in the future?
You
must plan for future growth. For example, if 9
subnets are
required today, and you choose to provide for 2
to the power of 4 = 16 subnets, this
might not be enough when the seventeenth subnet
needs to be deployed.
In this example, it might be wise to provide for
more growth and
select 2 to the power of 5 = 32 as the maximum
number of subnets.
-
What are the maximum
number of hosts on a given segment?
You
must ensure that there are enough bits available
to assign host
addresses to the organization’s largest subnet.
If the largest subnet needs to support 40 host
addresses today, 2 to the power of 5 =
32 will not provide enough host address space,
so you would need
to round up to 2 to the power of 6 = 64.
-
How many hosts will there
be in the future?
Besides planning for additional subnets, you
must also plan for more
hosts to be added to each subnet in the future.
Make sure the organization’s address allocation
provides enough
bits to deploy the required subnet addressing
plan.
When developing subnets, class C addresses
present the greatest
challenge because fewer bits are available to
divide between subnet
addresses and host addresses. If you accommodate
too many
subnets, there may be no room for additional
hosts and growth in
the future.
All the above points will help you succeed in
creating a well designed network which will have the
ability to cater for any additional future
requirements. And if you do happen to have any
problems, well, there is always the website's forum
where you can post your questions and problems :) |
