System Introduction
2–23
1070 072 262-101 (01.09) GB
Adjusting the Subnetwork Masks
The following two examples explain the adjustment of the subnetwork mask.
Example 1:
Subnetwork mask suitable
Determination of subnetwork address frontside
Subnetwork mask
255.255.192.0
11111111.
11111111.
11000000.
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
255.255.192.0
11111111.
11111111.
11000000.
00000000
IP address
backside
121.1.100.1
01111001.
00000001.
01100100.
00000001
Result of AND
operation corre-
sponds to sub-
network address
121.1.64.0
01111001.
00000001.
01000000.
00000000
With the subnetwork mask 255.255.192.0, the AND operation of the front-
and the backside delivers different results. Front- and backside do not be-
long to the same subnetwork. The addressing is unambiguous. The inter-
face is selected by comparing the target subnetwork with the existing
subnetworks.
Thus, with the subnetwork mask 255.255.192.0, the following IP addresses
can be addressed directly:
D
For the frontside: 121.1.[0 to 63].x
(x = 1 ... 254)
D
For the backside: 121.1.[64 to 127].y (y = 1 ... 254)