Important Terminology

The following terms are important for understanding virtual port extenders (VPEX):

• Bridge Port Extenders (BPEs)— Devices that do not fully process packets, nor make forwarding or filtering decisions. Instead, BPEs simply receive packets from extended ports and forward packets towards the upstream controlling bridge for L2/L3 processing.
• Cascade port—a port on a controlling bridge or BPE that connects to an upstream port.
• Controlling Bridge (CB)—In this context, a switch that provides full L2/L3 packet processing and filtering functionality for cascade ports and extended ports.
• E-Channel-ID (E-CID)—Identifies the BPE destination port (or port-list for multicast E-CID).
• E-Tag—A tag header immediately following the 802.1BR EtherType (0x893F) that contains the E-CID; this tag is only resident between bridge port extenders and controlling bridge devices.
• Edge Control Protocol (ECP)—Provides basic acknowledgement and re-transmission mechanism for reliable delivery; used for PE-CSP transmission.
• Extended bridge—A controlling bridge combined with one or more BPEs.
• Extended ports—Ports from BPEs connected to the rest of the network.
• Port Extender Control and Status Protocol (PE-CSP)—Simple command/response protocol that allows a controlling bridge to discover, program, and obtain status from a bridge port extender.
• Upstream port—Port on a BPE that connects to a cascade port.
• Virtual Port Extender (VPEX)—A switching architecture based on the IEEE 802.1BR specification, comprising a CB, and one or more BPEs.