Subnetting a 38 Network Address

The most important thing to remember when using a 24 bit subnet of our Class A 38 network is that it is *NOT* a real Class C network. Due to this fact it is easier to subnet than a Class C.

Remember that the subnet portion of an IP address cannot be all 0s or all 1's. Thus, when a Class C network is subnetted you cannot use a 1 bit subnet mask, since the subnet portion will either be 1 or 0 (which is all 1s and all 0s respectively). If you use a 2 bit subnet mask, you lose the 00 and 11 subnet and only the 01 and 10 subnets are usable.

The network portion of a Class A address is only 8 bits; the following 16 bits are part of the subnet portion of the address. If you add an additional bit to the subnet mask, then the number of subnet bits is 17 not 1. The subnet portion of the address is not 0 or 1 but xxxxxxxx xxxxxxxx 0 or xxxxxxx xxxxxxxx 1. This also follows for any number of subnet bits that are added. The only addressing space that is lost is the all 0s and all 1s hosts as these are still reserved for the network address, and broadcast address.

The following are the numbering schemes for the most common Subnet configurations for subnetting a 38.x.y.0 address:

25 Bit

Subnetwork Bits:         25
Number of Subnets:        2
Hosts per Subnet:       126
Total Number of Hosts:  252
Netmask:                255.255.255.128

Subnet 
Bits  Network  Range  Valid Hosts
------  -------  -----  -----------
0     0    0-127  1-126
1   128  128-255  129-254

26 Bit

Subnetwork Bits:         26
Number of Subnets:        4
Hosts per Subnet:        62
Total Number of Hosts:  248
Netmask:                255.255.255.192

Subnet 
Bits  Network  Range  Valid Hosts
------  -------  -----  -----------
0 0    0   0-63  1-62
0 1   64  64-127  65-126
1 0  128  128-191  129-190
1 1  192   192-255  193-254

27 Bit

Subnetwork Bits:  27
Number of Subnets:   8
Hosts per Subnet:  30
Total Number of Hosts: 240
Netmask:  255.255.255.224

Subnet 
Bits     Network         Range           Valid Hosts
------   -------         -----           -----------
0 0 0    0   0-31  1-30
0 0 1    32  32-63  33-62
0 1 0    64  64-95  65-94
0 1 1    96  96-127  97-126
1 0 0  128  128-159  129-158
1 0 1  160  160-191  161-190
1 1 0  192  192-223  193-222
1 1 1  224   224-255  225-254

28 Bit

Subnetwork Bits:         28
Number of Subnets:       16
Hosts per Subnet:        14
Total Number of Hosts:  224
Netmask:                255.255.255.240

Subnet
Bits     Network         Range           Valid Hosts
------   -------         -----           -----------
0 0 0 0    0   0-15  1-14
0 0 0 1   16  16-31  17-30
0 0 1 0   32  32-47  33-46
0 0 1 1   48  48-63  49-62
0 1 0 0   64  64-79  65-78
0 1 0 1   80  80-95  81-94
0 1 1 0   96  96-111  97-110
0 1 1 1  112  112-127  113-126
1 0 0 0  128  128-143  129-142
1 0 0 1  144  144-159  145-158
1 0 1 0  160  160-175  161-174
1 0 1 1  176  176-191  177-190
1 1 0 0  192  192-207  193-206
1 1 0 1  208  208-223  209-222
1 1 1 0  224  224-239  225-238
1 1 1 1  240   240-255  241-254

29 Bit

Subnetwork Bits:         29
Number of Subnets:       32
Hosts per Subnet:         6
Total Number of Hosts:  192
Netmask:                255.255.255.248

30 Bit

Subnetwork Bits:         30
Number of Subnets:       64
Hosts per Subnet:         2
Total Number of Hosts:  128
Netmask:                255.255.255.252