Reference Manual for the Model RP614 Web Safe Router
B-4 Network and Routing Basics
• ClassD
ClassD addresses are used for multicasts (messages sent to many hosts). Class D addressesare
in this range:
224.0.0.0 to 239.255.255.255.
• ClassE
Class E addressesare for experimental use.
Thisaddressing structure allows IP addresses to uniquely identify each physical network and each
node on eachphysical network.
For eachunique value of the network portion of the address, the base address of the range(host
addressof all zeros) is known as the network address and is not usually assigned to a host. Also,
the top addressof the range (host address of all ones) is not assigned, but is used as the broadcast
addressfor simultaneously sending a packet to all hosts with the same network address.
Netmask
In each of theaddress classes previously described, the size of the two parts (network address and
hostaddress) is implied by the class. This partitioning scheme can also be expressedby a netmask
associatedwith the IP address. A netmask is a 32-bit quantity that, when logicallycombined (using
an AND operator)with an IP address, yields the network address. For instance, the netmasks for
Class A, B, andC addresses are 255.0.0.0, 255.255.0.0, and 255.255.255.0, respectively.
For example,the address 192.168.170.237 is a Class C IP address whose network portion is the
upper24 bits. When combined (using an AND operator) with the Class C netmask,as shown here,
only the networkportion of the address remains:
11000000 10101000 10101010 11101101 (192.168.170.237)
combinedwith:
11111111 11111111 11111111 00000000 (255.255.255.0)
Equals:
11000000 10101000 10101010 00000000 (192.168.170.0)
As a shorteralternative to dotted-decimal notation, the netmask may also be expressed in terms of
thenumber of ones from the left. This number is appended to the IP address, followinga backward
slash (/ ), as “/n.” In the example, the address could be written as 192.168.170.237/24, indicating
that the netmask is 24 ones followedby 8 zeros.