Re: Subnetting 101

[samst@bdol10.indepth.com (Steve Sampson)]

There are many ways to subnet, but it depends on your frequency plan and
radio infrastructure.

Given a blank sheet - you probably want to do the following.  If your
infrastructure consists of Omni antennas and single frequency systems,
then don't bother to subnet - it won't help, and probably digipeating
would be more effective :-)

Take a string of numbers off one of the higher C octet list:

	44.42.64.x

Where x is 1, 2, 3, 4 etc and the backbone is seperate from the user
frequency.

This is unsophisticated subnetting.  It uses the C octet.  You could get
fancy and mask off bits for smaller subnets.

The user will route their packets on the user frequency to the local node
(say VHF).  This local node will then examine the destination address and
determine it is way up north, and route it via the backbone to its first
node on that path.  If it were south, then it would route it to the first
southern backbone node.  For most Ham uses, you don't need any more
sophistication than this.  The backbone nodes know what subnet is on the
VHF side because they are fixed into the routing table.  It either sends
it UHF to the next node, or out the VHF port for local users.

So basically the 64 leg is just a backbone pipe with tee's through filters
which connect it to local legs.

The local legs in Oklahoma have been subnetted by K5JB who is the state
admin for this.  His technique was simplified because Oklahoma County is
right in the middle of the state.  He then drew spokes and gave each space
between the spokes a seperate address range.  Another scheme is to subnet
by frequency: VHF is 0.x and UHF is 1.x etc.  That's basically what I've
done in my example, however I don't really suggest what the frequency is,
only that it be seperate from the user frequency.  I think Joe's (K5JB)
plan should be used as a model however.  The state topology should be used
to assign addresses FIRST, and then use what's left for frequency subnetting.
By having a 64 leg, that leaves 0 through 63 for user frequency routing.

For an excellent essay on subnetting read "The Hub 5/29 IP Routing Experiment"
by Paul Overton and Ian Wade in the 12th ARRL Digital Conference Proceedings.
It is more sophisticated than my example, and requires statewide coordination
(something most Hams refuse to do).
--
n5owk