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TR-Electronic GmbH 2018, All Rights Reserved
06/21/2018
TR - ELA - BA - DGB - 0028 - 00
Page 67 of 84
5.3.4 Combination IP-Address and Default Subnet mask
There is a declaration regarding the assignment of IP-address ranges and so-called
“Default Subnet masks”. The first decimal number of the IP-Address (from left)
determines the structure of the Default Subnet mask regarding the number of “1”
values (binary) as follows:
Net address range (dec.)
IP-Address (bin.)
Address
Class
Default
Subnet mask
1.0.0.0 - 126.0.0.0
0
xxx xxxx xxxx xxxx
xxxx xxxx
xxxx xxxx
A
255.0.0.0
128.1.0.0 - 191.254.0.0
10
xx xxxx xxxx xxxx
xxxx xxxx
xxxx xxxx
B
255.255.0.0
192.0.1.0 - 223.255.254.0
110
x xxxx xxxx xxxx xxxx xxxx xxxx xxxx
C
255.255.255.0
Class A-Net: 1 Byte Net address, 3 Byte Host address
Class B-Net: 2 Byte Net address, 2 Byte Host address
Class C-Net: 3 Byte Net address, 1 Byte Host address
Example Subnet mask
IP-Address = 130.094.122.195,
Net mask = 255.255.255.224
Decimal
Binary
Calculation
IP-Address
130.094.122.195
10000010 01011110 01111010 11000011
IP-Address
Net mask
255.255.255.224
11111111 11111111 11111111 111
00000
AND
Net mask
Net address
130.094.122.192
10000010 01011110 01111010 110
00000
= Net address
IP-Address
130.094.122.195
10000010 01011110 01111010 11000011
IP-Address
Net mask
255.255.255.224
11111111 11111111 11111111 111
00000
(00000000 00000000 00000000 000
11111
)
AND
(
NOT
Net mask)
Host address
3
00000000 00000000 00000000 000
00011
= Host address
