masking question

Hi,

I have the following table (it's from a book, not a real output):

Destination interface
0.1.0/18 eth0
0.2/12 eth1
etc

The (18) and (12) are masks, however, I don't understand to which part
of the address it applies. Does any one have a clue what the author
means ?
is 18 masked with the last 0, while 12 is maked with the 2 ?
Thank you great deal,
Alex

alexk wrote:
> Hi,
>
> I have the following table (it's from a book, not a real output):
>
> Destination interface
> 0.1.0/18 eth0
> 0.2/12 eth1
> etc

Both of the above are missing octets of the address. Ie.,
x.0.1.0 is miissing the first and x.x.0.2 is missing the first two.

> The (18) and (12) are masks, however, I don't understand to which
part
> of the address it applies. Does any one have a clue what the author
> means ?

This is called CIDR (Classless InterDomain Route notation) and the
number after the slash tells how many leading bits (of the 32 total)
make up the network address (yes, networks have IP addresses too).

> is 18 masked with the last 0, while 12 is maked with the 2 ?
> Thank you great deal,
> Alex

See eg.,
http://en.wikipedia.org/wiki/Classle...domain_routing
CIDR Notation
More info here:
http://infocenter.guardiandigital.co...DDS/node9.html
http://public.pacbell.net/dedicated/cidr.html

Google:
about 35,200 English pages for CIDR notation
hth,
prg
email above disabled

Thanks a lot, now it's clear.