Appendix B: Ip Address Information; Ip Address Nomenclature - CTI Janus 2500C-J Series Installation And Operation Manual

APPENDIX B: IP ADDRESS INFORMATION

IP Address Nomenclature

IP Address
Every host interface on a TCP/IP network is identified by a unique IP Address. This address is used to uniquely
identify the host device, such as a workstation or communications module, and the network to which the host
belongs.
Each IPV4 Address consists of 32 bits, divided into four 8 bit entities called octets. An IP Address is expressed in
dotted notation, with each octet expressed as its decimal equivalent. See the example below.
Notation
Binary
Decimal
Although an IP Address is a single value, it contains two types of information: the Network ID and the Host ID. The
Network ID identifies the IP network to which the host belongs. The Host ID identifies a specific IP host on that IP
network. All IP hosts on a particular local area network must have the same network ID. Each IP host on a
particular local area network must use a unique Host ID.
Address Classes
The Internet community originally defined network classes to accommodate networks of varying sizes. The
network class can be discerned from the first octet of its IP Address.
The following table summarizes the relationship between the first octet of a given address and its Network ID and
Host ID fields. It also identifies the total number of Network IDs and Host IDs for each address class that
participates in the Internet addressing scheme.
Class First Octet
Value*
A 1-126
B 128-191
C 192-223
* Address 127 is reserved for loopback testing and inter-process communication on the local computer; it is not a
valid network address. Addresses 224 – 239 are used for Class D (IP multicast).
CTI Janus Programmable Automation Controller IOG
Octet 1 Octet 2
11000000 11011111
192 223
Network ID Host ID
First Octet Last 3 Octets
First 2 Octets Last 2 Octets
First 3 Octets Last Octet
Octet 3 Octet 4
10110001 00000001
177 1
Number of Number of hosts
networks per net
126 16,777,214
16,384 65,534
2,097,151 254
69