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Full Discussion: Subnetting
Special Forums IP Networking Subnetting Post 302993549 by Scrutinizer on Saturday 11th of March 2017 03:36:20 AM
Old 03-11-2017
Say you have a class C network of 192.168.1.0/24 which has 254 usable host addresses, because 192.168.1.0 and 192.168.1.255 are not usable (2^8-2).

By changing the CIDR suffix to 25 , you create two networks:
Code:
192.168.1.0/25

and
Code:
192.168.1.128/25

The first has 126 usable host addresses (192.168.1.{1..126}, 2^7-2)
The second has 126 usable host addresses (192.168.1.{129..254}), 2^7-2)


--
The subnet mask of the /24 network is 255.255.255.0
The subnet mask of the two /25 networks is 255.255.255.128
This User Gave Thanks to Scrutinizer For This Post:
 

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WHOIS(1)						    BSD General Commands Manual 						  WHOIS(1)

NAME
whois -- Internet domain name and network number directory service SYNOPSIS
whois [-aAbfgiIklmPQrRS] [-c TLD | -h host] [-p port] [--] name ... DESCRIPTION
The whois utility looks up records in the databases maintained by several Network Information Centers (NICs). By default whois starts by querying the Internet Assigned Numbers Authority (IANA) whois server, and follows referrals to whois servers that have more specific details about the query name. The IANA whois server knows about IP address and AS numbers as well as domain names. There are a few special cases where referrals do not work, so whois goes directly to the appropriate server. These include point-of-contact handles for ARIN, nic.at, NORID, and RIPE, and domain names under ac.uk. The options are as follows: -a Use the American Registry for Internet Numbers (ARIN) database. It contains network numbers used in those parts of the world covered neither by APNIC, AfriNIC, LACNIC, nor by RIPE. The query syntax is documented at https://www.arin.net/resources/whoisrws/whois_api.html#nicname -A Use the Asia/Pacific Network Information Center (APNIC) database. It contains network numbers used in East Asia, Australia, New Zea- land, and the Pacific islands. Get query syntax documentation using whois -A help -b Use the Network Abuse Clearinghouse database. It contains addresses to which network abuse should be reported, indexed by domain name. -c TLD This is the equivalent of using the -h option with an argument of "TLD.whois-servers.net". This can be helpful for locating country- class TLD whois servers. -f Use the African Network Information Centre (AfriNIC) database. It contains network numbers used in Africa and the islands of the western Indian Ocean. Get query syntax documentation using whois -f help -g Use the US non-military federal government database, which contains points of contact for subdomains of .GOV. -h host Use the specified host instead of the default. Either a host name or an IP address may be specified. -i Use the traditional Network Information Center (InterNIC) (whois.internic.net) database. This now contains only registrations for domain names under .COM, .NET, .EDU. You can specify the type of object to search for like whois -i 'type name' where type can be domain, nameserver, registrar. The name can contain * wildcards. -I Use the Internet Assigned Numbers Authority (IANA) database. -k Use the National Internet Development Agency of Korea's (KRNIC) database. It contains network numbers and domain contact information for Korea. -l Use the Latin American and Caribbean IP address Regional Registry (LACNIC) database. It contains network numbers used in much of Latin America and the Caribbean. -m Use the Route Arbiter Database (RADB) database. It contains route policy specifications for a large number of operators' networks. -p port Connect to the whois server on port. If this option is not specified, whois defaults to port 43. -P Use the PeeringDB database of AS numbers. It contains details about presence at internet peering points for many network operators. -Q Do a quick lookup; whois will not attempt to follow referrals to other whois servers. This is the default if a server is explicitly specified using one of the other options or in an environment variable. See also the -R option. -r Use the R'eseaux IP Europ'eens (RIPE) database. It contains network numbers and domain contact information for Europe. Get query syntax documentation using whois -r help -R Do a recursive lookup; whois will attempt to follow referrals to other whois servers. This is the default if no server is explicitly specified. See also the -Q option. -S By default whois adjusts simple queries (without spaces) to produce more useful output from certain whois servers, and it suppresses some uninformative output. With the -S option, whois sends the query and prints the output verbatim. The operands specified to whois are treated independently and may be used as queries on different whois servers. ENVIRONMENT
WHOIS_SERVER The primary default whois server. If this is unset, whois uses the RA_SERVER environment variable. RA_SERVER The secondary default whois server. If this is unset, whois will use whois.iana.org. EXIT STATUS
The whois utility exits 0 on success, and >0 if an error occurs. EXAMPLES
To obtain contact information about an administrator located in the Russian TLD domain "RU", use the -c option as shown in the following example, where CONTACT-ID is substituted with the actual contact identifier. whois -c RU CONTACT-ID (Note: This example is specific to the TLD "RU", but other TLDs can be queried by using a similar syntax.) The following example demonstrates how to query a whois server using a non-standard port, where ``query-data'' is the query to be sent to ``whois.example.com'' on port ``rwhois'' (written numerically as 4321). whois -h whois.example.com -p rwhois query-data Some whois servers support complex queries with dash-letter options. You can use the -- option to separate whois command options from whois server query options. A query containing spaces must be quoted as one argument to the whois command. The following example asks the RIPE whois server to return a brief description of its ``domain'' object type: whois -r -- '-t domain' SEE ALSO
Ken Harrenstien and Vic White, NICNAME/WHOIS, 1 March 1982, RFC 812. HISTORY
The whois command appeared in 4.3BSD. BSD
April 25, 2016 BSD
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