TRENDnet TDM-E400 User's Guide - Page 187

field4 for its host IDs, ranging from 0 to 63., default subnet mask

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Note Appendix A. IP Addresses, Network Masks, and Subnets uses the remaining 7 bits in field4 for its host IDs, which range from 0 to 127 (instead of the usual 0 to 255 for a class C address). Similarly, to split a class C network into four subnets, the mask is: 255.255.255.192 or 11111111. 11111111. 11111111.11000000 The two extra bits in field4 can have four values (00, 01, 10, 11), so there are four subnets. Each subnet uses the remaining six bits in field4 for its host IDs, ranging from 0 to 63. Sometimes a subnet mask does not specify any additional network ID bits, and thus no subnets. Such a mask is called a default subnet mask. These masks are: Class A: Class B: Class C: 255.0.0.0 255.255.0.0 255.255.255.0 These are called default because they are used when a network is initially configured, at which time it has no subnets. 187

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Appendix
A
. IP Addresses, Network Masks, and Subnets
187
uses the remaining 7 bits in field4 for its host IDs, which range from
0 to 127 (instead of the usual 0 to 255 for a class C address).
Similarly, to split a class C network into four subnets, the mask is:
255.255.255.192
or
11111111. 11111111. 11111111.11000000
The two extra bits in field4 can have four values (00, 01, 10, 11), so
there are four subnets. Each subnet uses the remaining six bits in
field4 for its host IDs, ranging from 0 to 63.
Note
Sometimes a subnet mask does not specify any additional
network ID bits, and thus no subnets. Such a mask is called a
default subnet mask
. These masks are:
Class A:
255.0.0.0
Class B:
255.255.0.0
Class C:
255.255.255.0
These are called
default
because they are used when a network is
initially configured, at which time it has no subnets.