RMS Compact II
Version 1.0.7 September 2016
Page 57
The difference among the network classes is the number of octets reserved for the
network ID and the number of octets reserved for the host ID:
Class
Value of
First Octet
Network ID
Host ID
Number of
Hosts
A
1-126
first octet
last three
octets
16,387,064
B
128-191 first two oc-
tets
last two octets
64,516
C
192-223
first three
octets
last octet
254
Any value between 0 and 255 is valid as a host ID octet except for those values
reserved by the IPv4 standard for other purposes:
Value
Purpose
0, 255
Network Number & Broadcast
127
Loopback testing and interprocess communi-
cation on local devices
224-254
IGMP multicast and other special protocols
Subnetting and Subnet Masks
Subnetting divides a network address into subnetwork addresses to accommodate
more than one physical network on a logical network.
For example: A Class B company has 100 LANs (Local Area Networks) with 100 to
200 nodes on each LAN.
To classify the nodes by its LANs on one main network, this company segments the
network address into 100 subnetwork addresses (If the Class B network address is
150.1.x.x, the address can be segmented further from 150.1.1.x through 150.1.100.x.).
A subnet mask is a 32-bit value that distinguishes the network ID from the host ID for
different subnetworks on the same logical network.
Like IP addresses, subnet masks consist of four octets in dotted decimal notation.
You can use subnet masks to route and filter the transmission of IP packets among
your subnetworks.
The value “255” is assigned to octets that belong to the network ID, and the value “0”
is assigned to octets that belong to the host ID.
