Subnets (was: [dba-Tech] Modems)

A wonderful piece of work Drew, thank you!

Could I just enlarge on subnets?

Subnets (or subnetworks) are a way of subdividing a Local Area Network (LAN)
into smaller "groups". Subnets are formed by "borrowing" some of the "host"
part of the IP address.

For example:

Say you are using the private IP address 172.16.0.0 for your LAN. This would
give you useable host addresses from 172.16.0.1 to 172.16.255.254 (you
cannot use 172.16.0.0 as a host as this is the network number, and you
cannot use 172.16.255.255 as this is the broadcast address). This give you
65023 hosts.

If you "borrow" three bits from the host part of the address to form subnets
you get the following binary address format:

nnnnnnnn.nnnnnnnn.ssshhhhh.hhhhhhhh

where "n" are "network number" bits, "s" are subnet number bits, and "h" are
host number bits.

The subnet mask is used to signify which (if any) bits are used for subnet
addressing.

In the above example, the default subnet mask would be 255.255.0.0
This shows that only the first 16 bits are used in the network address.

If we "borrow" three bits for subnets the subnet mask will be 255.255.224.0,
because 224 in binary is 11100000.


Best regards!
Chris Foote


> -----Original Message-----
> From: Drew Wutka [mailto:dbatech at wolfwares.com]
> Sent: Wednesday, August 20, 2003 1:53 AM
> To: Discussion of Hardware and Software issues
> Subject: Re: [dba-Tech] Modems
> 
> 
> Steve, you asked, so I'm gonna learn ya!
>