Fluke 2680A User Manual page 254

2680A/2686A
Users Manual
Network subnets connected to the public Internet must obtain an official network
ID from a registrar approved by the Internet Network Information Center
(http://www.internic.net/) to preserve the unique network ID's within the Internet.
However, if you never intend to connect to the Internet, you're free to select your
own network IDs.
The IP address consists of four numbers. Each of these four numbers can have a
value in the range 1 to 254. An IP address is written in the form w.x.y.z. For
example, "198.178.246.10" (or "C6.B2.F6.0A" in hexadecimal) is a valid IP
address.
There are three commonly used classes of IP address assignment as follows:
Class w Value
A 1 to 126
B 128 to 191
C 192 to 223
The following are reserved addresses and may not be assigned to hosts:
127.0.0.0
128.0.0.0
191.255.0.0
192.0.0.0
223.255.255.0
w = 224 through 255 with x, y, and z equal to any value
Most IP subnets have Class B or C Net IDs because there are quite a few of these
available. You may be able to get a Class A Net ID, but there are so few of these
available (only 126 world-wide) that they are rarely issued and most are already
assigned.
Most companies get one or more Class C assignments, which means that there is a
limit of 254 hosts per network subnet.
The TCP/IP software separates the Net ID portion of the IP address from the Host
ID portion using the user-assigned Subnet Mask. This mask looks like an IP
address, but has a bit set in each bit position of the portion of the IP address that is
in the Net ID portion. For example, the Subnet Mask 255.255.255.0 sets the Net
ID portion to be the higher order 24 bits of the IP address (a class C address).
Using the Subnet Mask, the TCP/IP software is able to detect if a destination
address is in the local subnet or if the packet must be sent to another subnet
through a Router or Gateway.
H-6
Net ID Host ID
w x, y, z
w, x y, z
w, x, y z
Available Available Hosts
Subnets
126 16777214
16384 65534
2097151 254