Phoenix Contact FL WLAN 24 AP 802-11, Руководство пользователя

Страница: 54 / 122

Factory Line - Wireless LAN
3-20
PHOENIX CONTACT 7190_en_02
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.
3.5.2.2 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 generated from the user address and subnet mask. Because the masked subnetwork is
only recognized by the local computers, this extended IP address appears as a standard
IP address to all the other devices.
Structure of the subnet mask
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) 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 recognized by local
devices, the corresponding IP address appears as a "normal" IP address to all the other
devices.
Application
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.
Example for a Class B subnet mask:
Using this subnet mask, the TCP/IP protocol software differentiates between the devices
that are connected to the local subnetwork and the devices that are located in other
subnetworks.
Example: Device 1 wants to establish a connection with device 2 using the above subnet
mask. Device 2 has IP address 59.EA.55.32.
IP address representation for device 2:
2 5 5 . 2 5 5 . 1 9 2 . 0
1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 . 1 1 0 0 0 0 0 0 . 0 0 0 0 0 0 0 0
D e c i m a l n o t a t i o n :
B i n a r y n o t a t i o n :
S u b n e t m a s k b i t s
C l a s s B
5 9 . E A . 5 5 . 3 2
0 1 0 1 1 0 0 1 . 1 1 1 0 1 0 1 0 . 0 1 0 1 0 1 0 1 . 0 0 1 1 0 0 1 0
H e x a d e c i m a l n o t a t i o n :
B i n a r y n o t a t i o n :