CTI Products NCB/FL with Fiber Interface - Manual (Page 36)

CTI Products, Inc. NCB-EL/FL User Guide
Appendix F. IP Addresses 33
A
PPENDIX
F. IP A
DDRESSING
Conventions
Any node connected to an IP (Internet Protocol) network must be identified with a unique 32-bit address. These
32-bit addresses are commonly written in dotted decimal notation as four decimal numbers (referred to as octets
because each decimal number represents 8 bits) separated by decimal points. Each octet can be a number from
1 to 255. For example, 131.9.1.2 is a valid IP address. The IP address assigned to a network device is
commonly called the Host IP Address. By having unique addresses on a network, you can identify individual
stations (also called hosts or nodes) on the network.
The NCB-Etherlon and NCB-Fiberlon modules are provided from the factory with default addressing to allow
simple “quickstart” testing by connecting them back-to-back. See “A
PPENDIX A. F ACTORY D EFAULT
C ONFIGURATION ”.
IP Address Classes
There are five types of IP addresses. Three are associated with networks – Class A, B, and C.
• Class A addresses are for networks that have a large number of hosts, up to a maximum of 16,777,216
on a single IP network. The first octet is between 1 and 126. (127 is reserved for loopback and is used
for internal testing on the local machine.)
• Class B addresses are for medium-sized networks. The first octet is between 128 and 191.
• Class C addresses are for small networks, up to 255 hosts. The first octet is between 192 and 223.
• Class D addresses are reserved for multicasting and the first octet is between 224 and 239.
• Class E addresses (240 to 255) are reserved and should not be used.
An IP address consists of two parts – one part identifies the network, and one part identifies the host (or node).
The NetID portion of the IP address identifies the physical network segment. The HostID portion of the IP
address identifies the node within the network segment. The following table lists the capacities of each IP
address and the bits used as NetID and HostID.
IP
Class
Net ID
(Beginning Bits)
# of
Networks
Host ID
(Ending Bits)
# of Hosts or
Subnets
1 st byte
Range
A 8 126 24 16.7 million 1-126
B 16 16,000 16 65,000 128-191
C 24 2 million 8 254 192-293
Subnetting using Subnet Masks
A portion of the host bits can be used to “subnet the network”. The subnet mask identifies the “NetID” and
“HostID” portions of the IP address in a bitwise fashion. The mask is constructed by placing a “1” in any bit
that is part of a subnetwork address. So subnet mask bits that are SET define the NetID, and CLEARED subnet
mask bits define the HostID.
A subnet mask of 255.255.255.0 defines the NetID as the first three octets, and the HostID as the last octet. For
example, for the address 192.47.73.111 and the subnet mask of 255.255.255.0, the subnetwork can be
identified as 192.47.73.0.
Summary of Important Networking Details
• A specific “NetID” can exist on only ONE port of ONE IP router.
• The “NetID” portion of the Host Address and the Gateway Address MUST BE THE SAME.
• If a functional router (such as a NCB Router) is moved to a different location, its Host IP Address and
Default Gateway IP Address MUST BE CHANGED to match the “NetID” at the new location.