TCP/IP Configuration and Management Manual

NonStop TCP/IP Processes and Protocols
TCP/IP Configuration and Management Manual—427132-004
B-11
The Problem of Resolving Addresses
2. Once you’ve allocated the subnets, each office can assign their own local
addresses from within the range allocated to them for the subnet.
3. Once you’ve split the class B IP address for subnetting, determine the subnet
mask. Each ADD SUBNET command requires a subnet mask. The routing
algorithm residing in each host implements an OR operation on the subnet mask
and the destination to eliminate all but the relevant bits in the address. In all cases,
the first two octets are relevant; in our sample case, the first six bits of the second
octet are also relevant because they represent subnets. The mask is therefore:
11111111.11111111.11111100.00000000 (255.255.252.0). Figure B-8
shows the IP
address that results from the mask applied to the first subnet (Omaha’s). The
resulting IP address is 130.10.128.
Figure B-7. Omaha’s Subnets
Figure B-8. The Or Operation on the Mask and IP Address
026VST .VSD
10000000
Reserved for Subnets Reserved for Hosts
128
0
1
10
11
129
130
131
Subnet 0; Range 128 - 131.xx
11 1 0 0 0 0 0
Reserved for Subnets Reserved for Hosts
224
0
1
10
11
225
226
227
Subnet 24; Range 224 - 227.xx
Subnets 1 - 23; Ranges 132 - 223
027VST .VSD
11111111.11111111.11111100.00000000
10000010.00001010.10000000.00000011
or
10000010.00001010.10000000.00000000
130 10 128