3Com 10014299 manual IP address classes and ranges, Network IP network range Description Class

318CHAPTER 20: CONFIGURING IP ADDRESS

The IP addresses a user can use are listed in the following table.

Table 351 IP address classes and ranges

Network	IP network range	Description
class
A	1.0.0.0 ~ 126.0.0.0	Network IDs with all the digits being 0 or all the digits being
		1 are reserved for special use.
		Host ID with all the digits being 0 indicates that the IP
		address is the network address, and is used for network
		routing.
		Host ID with all the digits being 1 indicates the broadcast
		address, i.e. broadcast to all hosts on the network.
		Network ID 127 is used for self-loop interface.
B	128.1.0.0 ~	Network IDs with all the digits being 0 or all the digits being
	191.254.0.0	1 are reserved for special use.
		Host ID with all the digits being 0 indicates that the IP
		address is the network address, and is used for network
		routing.
		Host ID with all the digits being 1 indicates the broadcast
		address, i.e. broadcast to all hosts on the network.
C	192.0.1.0 ~	Network IDs with all the digits being 0 or all the digits being
	223.255.254.0	1 are reserved for special use.
		Host ID with all the digits being 0 indicates that the IP
		address is the network address, and is used for network
		routing.
		Host ID with all the digits being 1 indicates the broadcast
		address, i.e. broadcast to all hosts on the network.
D	None	Addresses of class D are multicast addresses.
		Host ID with all the digits being 1 indicates the broadcast
		address, i.e. broadcast to all hosts on the network.
E	None	255.255.255.255 is used as the whole network's broadcast
		address, and the other addresses are reserved for future use.

Important features of IP address:

Some IP addresses are not in a hierarchical structure, which is different from the structure of telephone number. In other words, these IP addresses cannot reflect any geographical information about the host position.

■When a host is connected to two networks at the same time (such as the host used as a router), it must have two corresponding IP addresses with different net-ids. Such host is called multihomed host.

■According to Internet concept, several LANs connected via transceiver or bridges are still in the same network, so these LANs have the same net-id.

■In terms of IP address, all networks which are assigned with net-ids are equal (no matter whether it is a small LAN or a big WAN).

Since 1985, only the net-id of IP address is assigned, while the following host-id is controlled by the enterprise. The IP address assigned to an enterprise is only a network ID: net-id. The specific host Ids, the host-ids for respective hosts, shall be assigned by the enterprise independently and uniquely. If there are many enterprise hosts widely scattered, the host IDs may be further divided into internal sub-nets to facilitate management. Please note that the division of sub-nets is