3Com Router 3000 Ethernet FamilyConfiguration Guide Chapter 4 Logical Interface Configuration3Com Corporation4-3Table 4-2 Create/delete a Null interfaceOperation CommandCreate a Null interface and enter the Null interface view interface null 0Delete the Null interface undo interface null 0As a Null interface drops all the packets reaching it, it provides you with a means ofpacket filtering. You can simply make the configuration to send all the undesirednetwork traffic to the interface Null0 rather than bothering yourself with the complexwork of configuring ACL (Access Control List).For example, you can drop all the packets destined to the segment 192.101.0.0 byconfiguring the static routing command ip route-static 192.101.0.0 255.255.0.0 null 0.4.4 Subinterface4.4.1 Introduction to SubinterfaceIntroducing the concept of subinterface into V 2.41 allows the users of 3Com SeriesRouters of high flexibility as the users can configure multiple subinterfaces on a singlephysical interface in this case.Subinterfaces are the logical virtual interfaces configured on a physical interface. Theyshare the physical layer parameters of the physical interface and can be separatelyconfigured with the link layer and network layer parameters. As they can be associatedwith a physical interface, they are often called “subinterfaces”.On 3Com Series Routers, the subinterface-supported physical interfaces include:z Ethernet interface. Without VLAN ID, an Ethernet subinterface can only supportIPX. Assigned with a VLAN ID, the subinterface can support both IPX and IP.z WAN interface encapsulated with FR. The subinterfaces of such a WAN interfacecan support both IP and IPX.z WAN interface encapsulated with X.25. The subinterfaces of such a WANinterface can support both IP and IPX.z IP-supported ATM subinterface4.4.2 Configuring an Ethernet SubinterfacePerform the following tasks to configure an Ethernet subinterface:z Create an Ethernet subinterfacez Configure encapsulation and VLAN ID on the subinterfacez Configure the maximum number of packets processed per second for a VLAN(optional)
