Wavetronix Click 342 (lean managed ethernet switch) (CLK-342) - Managed Switches User Guide - Manual (Page 18)

CHAPTER 1 • CLICK 340/341/342 MANAGED SWITCHES 17
˽ Value 255 in the Byte – Value 255 is defined as a broadcast address. The telegram is sent
to all the computers that are in the same part of the network. Examples: 004.255.255.255,
198.2.7.255 or 255.255.255.255 (all the computers in all the networks). If the network is
divided into subnetworks, the subnet masks must be observed during calculation, oth-
erwise some devices may be omitted. Simplified: The last address of an area is reserved
as the broadcast address.
˽ 0.x.x.x Addresses – Value 0 is the ID of the specific network. If the IP address starts
with a zero, the receiver is in the same network. Example: 0.2.1.1 refers to device 2.1.1
in this network. The zero previously signified the broadcast address. If older devices are
used, unauthorized broadcast and complete overload of the entire network (broadcast
storm) may occur when using the IP address 0.x.x.x.
Subnet Masks
Routers and gateways divide large networks into several subnetworks. The IP addresses for
individual devices are assigned to specific subnetworks by the subnet mask. The network
part of an IP address is not modified by the subnet mask. An extended IP address is gener-
ated from the user address and subnet mask. Because the masked subnetwork is only rec-
ognized by the local computers, this extended IP address appears as a standard IP address
to all the other devices.
The subnet mask always contains the same number of bits as an IP address. The subnet
mask has the same number of bits (in the same position) set to “one,” which is reflected in
the IP address for the network class.
Example
An IP address from Class A contains a 1-byte network address and a 3-byte computer
address. Therefore, the first byte of the subnet mask may only contain “ones.”
The remaining bits (three bytes) in the example above will then contain the address of the
subnetwork and the computer. The extended IP address is created when the bits of the IP
address and the bits of the subnet mask are ANDed. Because the subnetwork is only recog-
nized by local devices, the corresponding IP address appears as a “normal” IP address to all
the other devices.
If the ANDing of the address bits gives the local network address and the local subnetwork
address, the device is located in the local network. If the ANDing gives a different result, the
data telegram is sent to the subnetwork router.
Figure 2.3 below shows an example of a Class B subnet mask: