[Number of network addresses and host addresses supported]
Class
A
B
C
Network
scale
Large
Medium
Small
No. of network addresses
No. of host addresses
7
2 – 2 = approx. 16.77 million
14
2 – 2 = approx. 650,000
21
2 – 2 = 254
2 – 2 = 126
2 – 2 = approx. 160,000
2 – 2 = approx. 2.09 million
24
16
8
* For host addresses, “0” and “1” are always reserved for special purposes. Theren
fore the number of addresses is 2 – 2 (where “n” is the number of bits).
For network addresses, “0” and “1” are always reserved for special purposes on
n
RFC 950 compliant networks. Therefore the number of addresses is 2 – 2 (where
“n” is the number of bits). On RFC 1812 compliant networks, “0” and “1” are
always usable as a valid subnet. Therefore there is no need to subtract two.
Reference
JPNIC
The “JPNIC” is an organization that administers the NIC in Japan. It oversees
all administration for the assignment of
IP address and domain names in Japan. In order to make a corporate mail
server available or publish a Web server over the Internet, it is necessary to
apply for and acquire an IP address and
domain name from JPNIC.
Abbreviation for “Japan Network Information Center.”
Reference
NIC
The “NIC” is based in the United States,
and is the central governing body for
network information. It oversees all administration of IP addresses and supplies IP addresses.
Abbreviation for “Network Information
Center.”
Technology element
●Routing
A “router” is a device that connects multiple LANs and WANs to transfer
data between computers using the best path of transmission. A router corresponds to the network layer (Layer 3) in the OSI model.
The main function of a router is to perform “routing.” Routing is the process of transferring data using the best path of transmission so that the data
reaches the destination computer. Routers are positioned between computers engaged in communications and each one decides the next router to
send the data to, and relays the data. To decide on the next router, the router uses the destination IP address in the IP packet and searches for it in the
routing table within the router.
Routing is also referred to as “path control” and “path selection.”
An “RFC” is a document prepared by
the IETF ( Internet Engineering Task
Force) that describes technical information, specifications, and operating rules
concerning the Internet.
IETF is an organization that develops
standards for Internet technologies.
Abbreviation for “Request for Comments.”
Chapter 9
●Global IP address and private IP address
A “global IP address” is an IP address assigned to a computer that connects to the Internet. In order to connect to the Internet, it is necessary to
obtain a global IP address assigned by “JPNIC.”
A “private IP address” is an IP address assigned to a computer that only
connects to an individual network such as a corporate network. A private
IP address cannot be used to directly connect to the Internet.
Reference
RFC
Reference
Routing table
A “routing table” lists routing information
for the send destination of packets that
are managed by the router. Specifically,
a router stores a routing table that corresponds with the destination for received packets, and the networks or
router IP addresses through which the
packets are sent to the destination.
Routing tables can be generated and
managed via “static routing,” in which
the administrator of the router manually
configures each routing table, and “dynamic routing,” in which routers automatically configure routing tables by exchanging information between routers.
270