A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, such as the Internet, the computing devices communicate data by dividing the data into small blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assemblies the data into its original form. Dividing the data into packets enables the source device to resend only those individual packets that may be lost during transmission.
Certain network devices, such as routers, maintain tables of routing information that describe routes through the network. A “route” can generally be defined as a path between two locations on the network. Upon receiving an incoming data packet, the network device examines destination information within the packet to identify the destination for the packet. Based on the destination, the network device forwards the packet in accordance with the routing table.
A network device such as a router uses interface cards (IFCs) for receiving and sending data packets via network links. These IFCs are installed in ports known as interfaces and are configured using interface configurations. A network device can be manufactured with one or more interface configurations, including, for example, ATM, fast Ethernet, and Sonet interface configurations. In particular, a network device may include interface configuration for interfaces in which IFCs have been installed, as well as interfaces in which IFCs have not been installed. In addition, the network device may include a number of different configurations for a particular interface, enabling the network device to be preconfigured with a number of different upgrade paths.
When a new interface card is added to an interface in the network device, the interface is typically configured by selecting one of the pre-defined configurations that is appropriate for the type of interface card added to the interface. For example, if a fast Ethernet interface card is installed, a technician may select a pre-defined fast Ethernet configuration. Because this configuration already exists in the network device, it is not necessary for the technician to load the configuration, and installation is less complicated and time-consuming.
Before an interface card is installed in an interface, the interface can be considered a “phantom” interface in that it contains no interface card and is, as a result, inoperative. An interface may also be phantom after removal of a previously installed interface card whose configuration may remain loaded in the network device for potential use in a future installation of an interface card. An interface can also be phantom even if an interface card is installed, for example, if the network device stores multiple configuration options for the pertinent interface card slot. In particular, when the technician selects one of the configuration options, the other configuration options may remain stored in the network device. Generally, an interface can be considered phantom if it is associated with one or more interface card configurations that are not currently active.
The presence of a phantom interface may be confusing for installation technicians, network administrators, and other users who access the network device to obtain operational and configuration information. When such a user enters a command to display the configuration of the network device, the network device typically displays all of the configurations currently loaded in the network device, including those for phantom interfaces. This manner of presentation may confuse the user, particularly when multiple configuration options are loaded for a single interface. For example, when an interface card is installed, the user may have difficulty determining which configuration the technician selected for the interface card. Confusion may also arise if no interface card is physically installed in the interface. In particular, a user viewing the configuration may not be aware of the absence of an interface card without physically inspecting the network device interface.