03-11-2017
Hi,
To put it as simply as possible, in any given network range the very first address and the very last address are not usable for hosts. The first address is the network address, and the last address is the broadcast address.
So for 192.168.1.0/24 you'd have:
192.168.1.0 - Network address (NOT usable for hosts)
192.168.1.1 through 192.168.1.254 - Free IPs (Usable for hosts)
192.168.1.255 - Broadcast address (NOT usable for hosts)
And for /25 sub-nets (and all others besides) it'd be the same: the first address in the range and the last address in the range are not usable for hosts.
These 2 Users Gave Thanks to drysdalk For This Post:
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whois(1) General Commands Manual whois(1)
NAME
whois - Internet username directory service
SYNOPSIS
whois [-h server] name...
The whois command looks up user, host, and organization names in the Network Information Center (NIC) database.
OPTIONS
Specifies a whois server other than the default server rs.internic.net.
DESCRIPTION
The name argument can specify the following: The name of a registered user The name of a registered Internet host The name of some other
entity recognized by the whois server By default, the whois command queries the host rs.internic.net.
The operands specified to the whois command are concatenated together (separated by white-space) and presented to the whois the server.
The default action, unless directed otherwise with a special name is to do a very broad search, looking for matches to name in all types
of records and most fields (such as name, nicknames, host name, and network address) in the database. For more information as to what name
operands have special meaning, and how to guide the search, use the special name help.
EXAMPLES
To display the NIC database entry for the organization osf.org, enter: whois osf.org Open Software Foundation (OSF-DOM) 11 Cambridge Center
Cambridge, MAS 02142
Domain Name: OSF.ORG . . .
SEE ALSO
DARPA Internet Request for Comment: NICKNAME/WHOIS (RFC 812)
whois(1)