A subinterface is a logical interface on a physical interface such as the RPM ATM switch interface. Multiple subinterfaces can exist on a single physical interface.
A permanent virtual circuit (PVC) on the RPM is associated with a subinterface. You cannot terminate a PVC on the ATM switch interface. Some subinterfaces support multiple PVCs (multipoint); others support only one PVC (point-to-point). Figure 22-17 shows a multipoint subinterface and a point-to-point subinterface.
Figure 22-17 Multipoint and Point-to-Point Subinterfaces
A subinterface is assigned one IP address regardless of the number of PVCs that terminate on it. In order for multiple PVCs to terminate on one subinterface, the IP addresses of all meshed subinterfaces must be on the same network or subnetwork.
Figure 22-18 shows two subinterfaces on the RPM. Each subinterface is identified as chassis-slot/interface.subinterface. The chassis-slot is the RPM's card slot number, the interface is always 1, and the subinterface is a number that identifies the subinterface.
Figure 22-18 Subinterfaces on the RPM
In Figure 22-18, one of the subinterfaces is point-to-point (9/1.1), and the other is multipoint (9/1.2). Notice how all interfaces that terminate PVCs on a subinterface share the same IP network address. For example, 18.104.22.168, 22.214.171.124, and 126.96.36.199 are the IP addresses on interfaces attached to subinterface 2, which has an IP address of 188.8.131.52.