3Com 10014299 manual Sub-Interface

Any packet reaching the null interface will be dropped, which provides another method for packet filtering: Just sending unnecessary network traffic to Null0 interface, so that there is no need to configure ACL.

For example: Use static routing configuration command ip route-static 192.101.0.0 255.255.0.0 null 0 will drop all the packets sent to network segment 192.101.0.0.

Sub-Interface 157

2Configure operating parameters of the interface

ip unreachables is the only command which can be configured on the Null interface. It indicates that the router will reply the ICMP unreachable packet when it receives packets sent to the Null interface.

Please perform the following configurations in Null interface view.

Table 189 Configure/Remove the sending of ICMP unreachable packet

Operation	Command
Configure the sending of ICMP unreachable packet	ip unreachables
Remove the sending of ICMP unreachable packet	undo ip unreachables

Sub-Interface	The 3Com Router comes up with the concept of “sub-interface” and allows users
	to configure multiple sub-interfaces on one physical interfaces on the 3Com
	Router series, making it very flexible for configuration.
	Sub-interfaces refer to the multiple logical virtual interfaces configured on one
	physical interface. These virtual interfaces share the physical layer parameters of
	the physical interface, meanwhile, they can be configured with their own link layer
	parameters and network layer parameters. Therefore, the multiple virtual
	interfaces corresponding to one physical are called “sub-interfaces”.
	■ In the 3Com Router series, the physical interfaces supporting sub-interface
	features include:
	■ Ethernet interface: When the sub-interface of Ethernet has not been
	configured with VLAN id, the sub-interface can only support IPX network
	protocol. After configured with VLAN id, it will be able to support both IPX and
	IP protocols.
	■ WAN interface which link layer protocol is frame relay: Its sub-interface can
	support IP and IPX network protocols.
	WAN interface which link layer protocol is X.25: Its sub-interface can support IP
	and IPX network protocols.

Configure Sub-InterfaceAccording to different physical interfaces, sub-interface configuration includes:

■ Configure sub-interfaces of Ethernet interface

■ Configure sub-interfaces of WAN interface which link layer protocol is frame relay

■ Configure sub-interfaces of WAN interface which link layer protocol is X.25