regd. subnet mask

Can anyone please let me know :
Why should we use an "AND"
operator between subnet number and subnet mask?

On Fri, 01 Jun 2007, in the Usenet newsgroup comp.os.linux.networking, in
article <(E-Mail Removed). com>,
(E-Mail Removed) wrote:

>Can anyone please let me know :
> Why should we use an "AND"
>operator between subnet number and subnet mask?

Well, you could ask your instructor - or you could grab a copy of
the Linux Network Administrator's Guide from the LDP at
http://tldp.org/guides.html - try either

* The Linux Network Administrator's Guide, Second Edition
version: 1.1
authors: Olaf Kirch and Terry Dawson
last update: March 2000
ISBN: 1-56592-400-2
available formats:
1. HTML (read only) 2. HTML (tarred and gzipped package, 690k)
3. PDF (1.5MB)

or

* The Linux Network Administrators' Guide
version: 1.0
author: Olaf Kirch
last update: March 1996
available formats:
1. HTML (read online) 2. HTML (tarred and gzipped package, 332k)
3. other : plain text, DVI, LaTeX source, PDF, and PostScript.
4. various (non-English) translations

and if it's not obvious, then use that search engine you are posting from
to find a copy of RFC0950 and RFC1878

0950 Internet Standard Subnetting Procedure. J.C. Mogul, J. Postel.
August 1985. (Format: TXT=37985 bytes) (Updates RFC0792) (Also
STD0005) (Status: STANDARD)

1878 Variable Length Subnet Table For IPv4. T. Pummill, B. Manning.
December 1995. (Format: TXT=19414 bytes) (Obsoletes RFC1860) (Status:
HISTORIC)

The key concept is the logical AND

Address 1 192.168.0.15 1100 0000 1010 1000 0000 0000 0000 1111
Netmask 255.255.255.0 1111 1111 1111 1111 1111 1111 0000 0000
Address 2 192.168.2.158 1100 0000 1100 0000 0000 0010 1001 1110
Match? yyyy yyyy yyyy yyyy yyyy yyN

The two don't match where there is a '1' in the network mask - therefore
they aren't on the same network.

Old guy