[Dshield] Another simple question...

Jeff Miller jrm.wa at verizon.net
Sun Oct 28 17:22:00 GMT 2001


That's called the bitmask.  It refers to bits of subnetting.  Some common
subnets you'll see are:

/8 - 255.0.0.0 = 11111111.00000000.00000000.00000000 = 8 1's = FF.00.00.00
/16 = 255.255.0.0 = 11111111.11111111.00000000.00000000 = 16 1's =
FF.FF.00.00
/24 = 255.255.255.0 = 11111111.11111111.11111111.00000000 = 24 1's =
FF.FF.FF.00
/30 = 255.255.255.252 = 11111111.11111111.11111111.11111100 = 30 1's =
FF.FF.FF.FC

It's just another way of representing a subnet mask called Classless
Inter-Domain Routing (CIDR).

Hope that helps.

-----Original Message-----
From: dshield-admin at dshield.org [mailto:dshield-admin at dshield.org]On
Behalf Of Josh Tolley
Sent: Saturday, October 27, 2001 4:47 PM
To: dshield at dshield.org
Subject: [Dshield] Another simple question...


What does the /8, /12, etc. below mean?  I assume subnet, but having
only used 4 octet notation for subnets, I don't know how to translate
it.

Josh Tolley

<snip>
The reserved-for-private-use netblocks should be blocked in *both
directions* (in and out, source and destination) at your boundary:
10.0.0.0/8
172.16.0.0/12
192.168.0.0/24
</snip>


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