Cabletron Systems EMM-E6 Ethernet - Manual (Page 37)

REVIEW OF ADDRESSING
EMM-E6 User’s Guide 1-25
1.10.3 Identifying IP Address Classes
In the event that you have an existing IP address and need to quickly
determine what fields are available for Host IP address configuration,
make that determination based on the binary value of the first DDN field.
Tables 1-1 to 1-3 show that different address classes have different initial
bits in the first octet. A Class A address, for example, will always have a
zero as the first bit of the first octet. To identify an IP address’ class,
convert the decimal value of the first DDN field to binary.
Example: 132.177.118.24
Convert first DDN field to binary: 132
10
= 10000100
2
Since the first two bits of the octet are 10
2
, the address is Class B. Refer to
the IP address Classes tables, each Class B address utilizes the first two
fields for a Network ID (132.177.118.24), while the remaining two fields
(132.177.118.24) are the Host ID.
1.10.4 Subnet Addresses
Subnet addresses are used to partition an IP network into multiple
subnetworks or subnets. The use of subnet addresses adds an additional
layer of hierarchy to the IP addressing scheme. This additional addressing
layer facilitates isolation, control, and administration of users within the
network, at a cost of reduction in total available Host IDs. This is done by
grouping hosts into separate subnets. To use the above Class B address,
132.177.118.24, as an example, the last two fields are available for the
assignment of Host IDs. If the Network Manager desired to use subnets,
the third field, 118, could become common to a series or group of hosts
with a common physical location or intended purpose.
Example (Class B):
132.177.118.24
{
{
{
Net ID Host ID
Subnet Number Host Number
{
CH1Book Page 25 Wednesday, March 20, 1996 7:48 AM