Startup and functions
6874_en_16
PHOENIX CONTACT
3-7
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:
The individual subnet mask and the IP address for device 2 are then ANDed bit-by-bit by the
software to determine whether device 2 is located in the local subnetwork.
ANDing the subnet mask and IP address for device 2:
After ANDing, the software determines that the relevant subnetwork (01) does not
correspond to the local subnetwork (11) and the data telegram is forwarded to a subnetwork
router.
255.255.192.0
1111 1111.1111 1111.1100 0000.0000 0000
Decimal representation:
Binary representation:
Subnet mask bits
Class B
61462010
59.EA.55.32
0101 1001.1110 1010.0101 0101.0011 0010
Hexadecimal representation:
Decimal representation:
61462011
1111 1111.1111 1111.1100 0000.0000 0000
0101 1001.1110 1010.0101 0101.0011 0010
0101 1001.1110 1010.0100 0000.0000 0000
Subnet mask:
IP address:
Result:
AND
Subnetwork
61462012
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