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Full Discussion: Subnetting
Special Forums IP Networking Subnetting Post 302993570 by drysdalk on Saturday 11th of March 2017 07:41:05 AM
Old 03-11-2017
Hi,

Firstly, from just looking at a single IP, you can't tell how large the network it's a part of is. You need to know the netmask. So for example, if I had an IP of 192.168.1.10, that doesn't tell you anything at all about how large or small the network I'm a part of is.

But if I tell you the netmask - e.g. 192.168.1.10/24 or 192.168.1.10/255.255.255.0 - then you know it's part of a network of 256 addresses, running from 192.168.1.0 to 192.168.1.255.

If on the other hand I'd told you the netmask was 192.168.1.10/25 or 192.168.1.10/255.255.255.128 - then you'd know it was part of a network of 128 addresses going from 192.168.1.0 to 192.168.1.127.

And again, in every network, the very first address and the very last address are not usable for hosts, as they are reserved for other purposes.

You can also get plenty of other netmasks than the old simple Class A, B, C notation tells you. For instance I could just have easily told you my netmask was 192.168.1.10/28, in which case you'd then be able to calculate that the network I was a part of runs from 192.168.1.0 to 192.168.1.15, and conists of 16 IP addresses.

So just from looking at an IP you can't tell anything about the size of the network. And these days, there are far more netmasks and subnet sizes that are far more common than the old Class A/B/C notation.
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LEARN ABOUT DEBIAN

cwhois

CWHOIS(3)							   whois client 							 CWHOIS(3)

NAME

       CWHOIS - whois client

SYNOPSIS

       cwhois [-a|-F|-L|-m|-M|-r|-S|-R] [-h hostname] [-s source[[,source]...]] [-T type[[,type]...]] [-i attr[[,attr]...]] keys

       cwhois [-t type]

       cwhois [-v type]

DESCRIPTION

       cwhois Simple whois client that gives you back output, compatiable with RIPE DB v2, if you'll ask it to.

OPTIONS

       -a     search all databases

       -F     fast raw output

       -L     find all Less specific matches

       -m     find first level more specific matches

       -M     find all More specific matches

       -r     turn off recursive lookups

       -S     tell server to leave out 'syntactic sugar'

       -R     force to show local copy of the domain object even if it contains referral

       -h hostname
	      search alternate server

       -s source[[,source]...]
	      search databases with source 'source'

       -T type[[,type]...]
	      only look for objects of type 'type'

       -i attr[[,attr]...]
	      do an inverse lookup for specified attributes

       -t type
	      requests template for object of type 'type'

       -v type
	      requests verbose template for object of type 'type'

HINT

       Please note that most of these flags are NOT understood by non RIPE whois servers!

SEE ALSO

       Website <http://www.ripe.net/tools/>

AUTHOR

       CWHOIS was written by Timur Bakeyev <timur@ripe.net>.

       This manual page was written by Jan Wagner <waja@cyconet.org>, for the Debian project (but may be used by others).

1.10								    2006-11-03								 CWHOIS(3)
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