System Introduction
2–24
1070 072 262-101 (01.09) GB
Example 2:
Subnetwork mask not suitable
Determination of subnetwork address frontside
Subnetwork mask
255.255.0.0
11111111.
11111111.
00000000.
00000000
IP address
frontside
121.1.1.1
01111001.
00000001.
00000001.
00000001
Result of AND
operation corre-
sponds to sub-
network address
121.1.0.0
01111001.
00000001.
00000000.
00000000
Determination of subnetwork address backside
Subnetwork mask
255.255.0.0
11111111.
11111111.
00000000.
00000000
IP address
backside
121.1.64.1
01111001.
00000001.
10000000.
00000001
Result of AND
operation corre-
sponds to sub-
network address
121.1.0.0
01111001.
00000001.
01000000.
00000000
Do not use the subnetwork mask 255.255.0.0 because with the result of the
AND operation front- and backside cannot distinguish. Front- and backside
belong to the same subnetwork. Unambiguous addressing is not possible.
.
Also the local network card must present an IP address in the same
subnetwork if the PC is to be linked directly to the subnetwork.
Communication via the IP addresses will be established as follows:
D
If the network stations are located in the same subnetwork, the communi-
cation packets will be exchanged directly.
D
If the IP address is located in another subnetwork, the data packets will
be forwarded via the router (computer that connects different network
segments with each other). I.e., that if there is no router in the network,
communication is not possible.
Example:
Computer address:
142.2.30.70
Subnetwork mask:
255.255.0.0
Subnetwork router address: 142.2.0.100
Target address:
142.3.12.7
–> Data packet to router
Target address:
142.2.20.21
–> Data packet remains in
its own subnetwork
