Special Address Facts

Special Address Facts

You should understand the following special addresses:

Address	Consideration
Network	The first octet(s) in an address range is used to identify the network itself. For the network address, the host portion of the address contains all 0's. For example: Class A network address: 115.0.0.0 Class B network address: 154.90.0.0 Class C network address: 221.65.244.0 0.0.0.0 is the network address used by routers to specify the "default" route. Using a generic value reduces the number of routing table entries. Some older routers use this address as a broadcast address.
Host	The range of IP addresses available to be assigned to network hosts is identified by the subnet mask and/or the address class. For example: For the class A network address 115.0.0.0, the host range is 115.0.0.1 to 115.255.255.254. For the class B network address 154.90.0.0, the host range is 154.90.0.1 to 154.90.255.254. For the class C network address 221.65.244.0, the host range is 221.65.244.1 to 221.65.244.254. Note: A special way to identify a host on a network is by setting the network portion of the address to all 0's. For example, the address 0.0.64.128 means "host 64.128 on this network."
Broadcast	The last address in the range is used as the broadcast address and is used to send messages to all hosts on the network. In binary form, the broadcast address has all 1's in the host portion of the address. For example, assuming the default subnet masks are used: 115.255.255.255 is the broadcast address for network 115.0.0.0 154.90.255.255 is the broadcast address for network 154.90.0.0 221.65.244.255 is the broadcast address for network 221.65.244.0 Two other formats you might see for the broadcast address: The broadcast address might also be designated by setting each of the network address bits to 0. For example, 0.0.255.255 is the broadcast address of a Class B address. This designation means "the broadcast address for this network." 255.255.255.255 indicates a broadcast message intended for all hosts on this network.
Local host	Addresses in the 127.0.0.0 range are reserved for the local host (in other words "this" host or the host you're currently working at). The most commonly-used address is 127.0.0.1 which is the loopback address.
Private use	The following address ranges have been reserved for private use: 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255 Use addresses in these ranges for your private networks. Routers connected to the Internet typically filter messages within these ranges and prevent them from being propagated to the Internet.