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DI-206 ISDN Remote Router
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Appendix B - IP Concepts
This appendix describes some basic IP concepts, the TCP/IP addressing scheme and show how to assign IP Addresses.
When setting up the router, you must make sure all ports to be utilized on the router have valid IP addresses. Even if you will
not use the ISDN or WAN ports, you should, at the very least, make sure the LAN port is assigned a valid IP address. This is
required for telnet, in-band SNMP management, and related functions such as “trap” handling and TFTP firmware download.
IP Addresses
The Internet Protocol (IP) was designed for routing data between network sites all over the world, and was later adapted to
allow routing between networks (often referred to as “subnets”) within any site. IP includes a system by which a unique
number can be assigned to each of the millions of networks and each of the computers on those networks. Such a number is
called an IP address.
To make IP addresses easy to understand, the originators of IP adopted a system of representation called “dotted decimal” or
“dotted quad” notation. Below are examples of IP addresses written in this format:
201.202.203.204 189.21.241.56 125.87.0.1
Each of the four values in an IP address is the ordinary decimal (base 10) representation of a value that a computer can handle
using eight “bits” (binary digits — 1s and 0s). The dots are simply convenient visual separators.
Zeros are often used as placeholders in dotted decimal notation; 189.21.241.56 can therefore also appear as 189.021.241.056.
IP networks are divided into three classes on the basis of size. A full IP address contains a network portion and a “host”
(device) portion. The network and host portions of the address are different lengths for different classes of networks, as shown
in the table below.
Networks attached to the Internet are assigned class types that determine the maximum number of possible hosts per network.
The previous figure illustrates how the net and host portions of the IP address differ among the three classes. Class A is
assigned to networks that have more than 65,535 hosts; Class B is for networks that have 256 to 65534 hosts; Class C is for
networks with less than 256 hosts.
IP Network Classes
Class Maximum
Number of
Networks in
Class
Network Addresses (Host
Portion in Parenthesis)
Maximum
Number of
Hosts per
Network
A
126 1(.0.0.0) to 126(.0.0.0) 16,777,214
B
16,382 128.1(.0.0) to 191.254(.0.0) 65,534
C
2,097,150 192.0.1(.0) to 223.255.254(.0) 254