The IP Manager permits performance monitoring of sub-interfaces. If you intend to monitor the sub-interfaces using the IP Performance Manager, each sub-interface must be counted as an interface and added to your total of managed ports and interfaces.
The quantity of sub-interfaces is very difficult to estimate: for example, some Cisco devices permit you to configure thousands of sub-interfaces. If your network uses technologies such as frame relay, ATM, or ISDN, pay particular attention to the sub-interface configurations. Consult network administrators to determine a reasonable maximum quantity of sub-interfaces.