3Com 5500G, 4210, 4200G manual That they can communicate with each other

28CHAPTER 3: IP ADDRESS CONFIGURATION GUIDE

Configuration Procedure	Assign a primary and secondary IP addresses to VLAN-interface 1 of Switch to
	ensure that all the hosts on the LAN can access external networks through Switch.
	Set Switch as the gateway on all the hosts of the two network segments to ensure
	that they can communicate with each other.
	# Assign a primary IP address and a secondary IP address to VLAN-interface 1.
	<Switch> system-view
	[Switch] interface Vlan-interface 1
	[Switch-Vlan-interface1] ip address 172.16.1.1 255.255.255.0
	[Switch-Vlan-interface1] ip address 172.16.2.1 255.255.255.0 sub
	# Set the gateway address to 172.16.1.1 on the hosts in subnet 172.16.1.0/24,
	and to 172.16.2.1 on the hosts in subnet 172.16.2.0/24.
	# Ping Host B on Host A to verify the connectivity.
Complete Configuration	#
	interface Vlan-interface 1
	ip address 172.16.1.1 255.255.255.0
	ip address 172.16.2.1 255.255.255.0 sub
	#
Precautions	■ You can assign at most five IP addresses to an interface, among which one is
	the primary IP address and the others are secondary IP addresses. A newly
	specified primary IP address overwrites the previous one.
	■ The primary and secondary IP addresses of an interface cannot reside on the
	same network segment; an IP address of a VLAN interface must not be on the
	same network segment as that of a loopback interface on a device.
	■ A VLAN interface cannot be configured with a secondary IP address if the
	interface has obtained an IP address through BOOTP or DHCP.