Techniques for processing packets in a network device include using a configuration table to determine a key corresponding to a packet. The configuration table may be indexed based on contents of a field of the packet (e.g., e/port or e/VLAN) to find a corresponding entry indicating a key format. When a key extension indicator has a first pre-determined value, a key extension field is added to the key format, and when the key extension indicator has a second pre-determined value, the key extension indicator is excluded from the key format. The populated key format or key (including any key extension field, if so determined) is used to determine a processing action for the packet. Key extension indicators support compatibility with non-legacy devices that utilize extended fields in packets, and with legacy devices. Embodiments of methods and network devices that support standard and extended keys are disclosed.