Analysis of a commercial DSL Order - subnetting

network/netmask summary: or equivalently

"Range  .226-.254" suggests that (with adjustments) the size of this network is 32 addresses. That corresponds to a netmask with 5 rightmost 0 digits from which to compose host addresses (since from 5 digits 32 distinct values can be composed). The netmask is therefore:

 11111111 11111111 11111111 11100000, or

One of the addresses will be reserved for the ISP-supplied gateway. Since the Gateway address given is, we know that the first 3 dot-quad values for all our network's addresses must be 64.52.25.

The address of the network (here called "subnet") must be aligned on an address boundary that is a multiple of the network's extent, or size, which is 32. So the possible 4th dot-quad elements of the network addresses would be 0, 32, 64, 96, 128, 160, 192, 224. Among these, "Subnet:  .224" is our clue that our network (i.e., the first of its addresses) lies at 224, or more precisely at (It is coincidence that the measure of the network's extent,, also happens to contain "224")

Of these, 2 are reserved and 30 are available for assignment to hosts (computers). And of the 30, one is taken by the "Gateway." That one happens to be (but could be any of the other 29). - reserved, functions as the address of this network itself - assigned to the ISP-supplied Gateway - reserved, functions as the "broadcast" address to which all hosts in this network will respond in addition to their own address

It's useful to think of these networks or subnets as being defined by a position, and an extent measured from that position, on the continuum of IP addresses represented as a number line. Of the parameters supplied by ISPs, it is the so-called network address that establishes the position or starting point of the address range or block. And it is the netmask that establishes its extent or size. In this case the network address is and the netmask is (coincidence that they both end with 224). The number line below is a microscopic segment of the number line for the whole internet. That number line is 4 billion addresses in length (because with 32 bits 4 billion is the number of distinct address values that can be composed). Here, with the first 24 bits of our address (64.52.25) we are narrowing in on a particular little 256-address segment within that number line. Within the segment, the network address further positions us with final precision. This idea of sectioning off the 4 billion addresses into separately addressable subordinate pieces is called subnetting, and the resulting pieces or address groups are called subnets.