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* Explanation [1]
* Calculators [2]
* Melbourne Wireless Subnets [3]
EXPLANATION
A SUBNET IS A SUBDIVISION OF A TCP/IP [4] NETWORK.
Subnets can be large or small, but generally, smaller subnets make
for more efficient Routing [5].
As an example, say you had a private TCP/IP network with the address
range:
192.168.0.0 - 192.168.255.255. This gives you 65536 addresses. If you
had that many devices on your network you would probably be swamped
with Broadcast [6] traffic and things would slow to a crawl.
Your network or subnet is defined by its SUBNET MASK or NETMASK.
In the example above your netmask is
255.255.0.0 - in Windows terminology
192.168.0.0/16 - in Unix terminology
The parts in BOLD are the actual netmask specification.
The first IP address of your subnet is always the NETWORK ADDRESS and
the last IP address is almost always the BROADCAST ADDRESS. These are
special addresses reserved by the TCP/IP protocol for doing special
things. That means you always have two less IP addresses that you can
use for your devices than what your netmask specifies.
In the above example the Network address is 192.168.0.0 and the
Broadcast Address is 192.168.255.255. That leaves you with 65534
addresses.
Suppose you wanted to subdivide a part off of the very large subnet
in the above example. You could start your new subnet with the address
192.168.1.0. If you wanted 256 addresses your netmask would be:
255.255.255.0 or 192.168.1.0/24.
If you wanted another, even smaller subnet somewhere else in the
larger address range above, say 16 addresses, and you wanted the
address
192.168.70.45 to be within that address range (for whatever reason).
Your netmask would be
255.255.255.240 or 192.168.70.32/28
192.168.70.32 would be your Network Address
192.168.70.47 would be your Broadcast Address
CALCULATORS
These numbers were calculated using the online subnet calculator at
http://www.telusplanet.net/public/sparkman/netcalc.htm [7].
There are also various free subnet calculators for Windows and Linux
downloadable from the net. Google [8] will find them for you.
If you run the Shorewall firewall [9] available for Linux then an
ipcalc command has been available since version 1.4.6
IPCALC [ | / ]
Example:
root@wookie:# shorewall ipcalc 10.10.144.48/28 CIDR=10.10.144.48/28
NETMASK=255.255.255.240 NETWORK=10.10.144.48 BROADCAST=10.10.144.63
MELBOURNE WIRELESS SUBNETS
From LocFinder [10], MELBOURNE WIRELESS nodes are allocated subnets
from the 10.10.0.0/16 address range. Upon request, individual nodes
are given /28 subnets giving them 14 usable addresses per subnet. In
the near future, nodes may request smaller subnets if they wish.
Links:
------
[1] http://melbournewireless.org.au/#explanation
[2] http://melbournewireless.org.au/#calculators
[3] http://melbournewireless.org.au/#melbourne_wireless_subnets
[4] http://melbournewireless.org.au/?TCPIP
[5] http://melbournewireless.org.au/?Routing
[6] http://melbournewireless.org.au/?Broadcast
[7] http://www.telusplanet.net/public/sparkman/netcalc.htm
[8] http://www.google.com.au
[9] http://www.shorewall.net/
[10] http://melbournewireless.org.au/?LocFinder
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