3Com Router 3000 Ethernet FamilyConfiguration Guide Chapter 4 Logical Interface Configuration3Com Corporation4-2I. Creating a loopback interfaceTable 4-1 Create/delete a loopback interfaceOperation CommandCreate a loopback interface and enterthe loopback interface view interface loopback numberDelete the specified loopback interface undo interface loopback numberII. Configuring the operating parameters of the interfaceYou can configure the parameters like IP address and IP routing for a loopbackinterface. For details, refer to V 2.41 Operation Manual - Network Protocol.Caution:You can configure a 32-bit subnet mask for a loopback interface. that is, the subnetmask can be 255.255.255.255. In addition, the IP address with the 32-bit mask can beadvertised through a routing protocol.You are recommended to assign a host address of 32-bit mask to a loopback interface.In this way, you can not only save the address resources but also use the interface asan unnumbered interface.You can use the shutdown command to disable the loopback interface.4.3 Null Interface4.3.1 Introduction to Null Interface3Com Series Routers support the Null interface. Such an interface is always UP butcannot forward packets. In addition, no IP address or other link layer protocols can beconfigured on it.Null interface is the logical interface of pure software property. Therefore, all thenetwork specific packets sent to the interface will be dropped.4.3.2 Configuring a Null InterfacePerform the following configuration in system view to create the interface Null 0 on a3Com router.
