3Com WX3000 operation manual Configuring IP Addresses, Ip address ip-address mask, Mask-length sub

adds an additional level, subnet ID, to the two-level hierarchy with IP addressing, IP routing now involves three steps: delivery to the site, delivery to the subnet, and delivery to the host.

In the absence of subnetting, some special addresses such as the addresses with the net ID of all zeros and the addresses with the host ID of all ones, are not assignable to hosts. The same is true of subnetting. When designing your network, you should note that subnetting is somewhat a tradeoff between subnets and accommodated hosts. For example, a Class B network can accommodate 65,534 (216 – 2. Of the two deducted Class B addresses, one with an all-ones host ID is the broadcast address and the other with an all-zeros host ID is the network address) hosts before being subnetted. After you break it down into 512 (29) subnets by using the first 9 bits of the host ID for the subnet, you have only 7 bits for the host ID and thus have only 126 (27 – 2) hosts in each subnet. The maximum number of hosts is thus 64,512 (512 × 126), 1022 less after the network is subnetted.

Class A, B, and C networks, before being subnetted, use these default masks (also called natural masks): 255.0.0.0, 255.255.0.0, and 255.255.255.0 respectively.

Configuring IP Addresses

The device supports assigning IP addresses to VLAN interfaces and loopback interfaces. Besides directly assigning an IP address to a VLAN interface, you may configure a VLAN interface to obtain an IP address through BOOTP or DHCP as alternatives. If you change the way an interface obtains an IP address, from manual assignment to BOOTP for example, the IP address obtained from BOOTP will overwrite the old one manually assigned.

This chapter only covers how to assign an IP address manually. For the other two approaches to IP address assignment, refer to the part discussing DHCP in this manual.

Follow these steps to assign an IP address to an interface:

To do…		Use the command…	Remarks
Enter system view		system-view	––
Enter interface view		interface interface-type	––
		interface-number
Assign an IP address to the		ip address ip-address { mask	Required
			No IP address is assigned by
interface	mask-length } [ sub ]
			default.

1-3