The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

12.2. Elements of the Standard

802.1Q provides, at a minimum, all of the functionality, features, and capabilities of 802.1D. Thus, the standard provides:

• An architecture for transparent bridging among an arbitrary number of ports attached using any MAC technology that supports 48-bit globally unique addresses (Ethernet, Token Ring, FDDI, and so on)

• An architecture for a filtering database, that is, a data structure that allows the bridge to know the mapping of devices to ports

• The algorithms for filtering and forwarding frames among the ports, based on the contents of the filtering database

• The algorithms for learning and aging entries in the filtering database

• Optionally, the capability to support multicast pruning and priority operation, as discussed in Chapter 10, "Multicast Pruning," and Chapter 13, "Priority Operation," respectively^[]

  ^[] As with a D-compliant device, a Q-compliant bridge can implement either or both multicast pruning and traffic class expediting; these functions are orthogonal to its VLAN capabilities.

• A specification for the Spanning Tree Protocol to prevent active loops in the catenet

• A standard set of objects [Management Information Base (MIB)] for vendor-interoperable management of bridges

To support the VLAN-related operations of a switch, 802.1Q extends the 802.1D functionality in a number of areas:

• Filtering database: A D-compliant filtering database only provides the means to map 48-bit addresses to ports. This was all that was needed for basic bridge operation. ...