Industrial Connectivity Introducing Basic Layer 2 Switching and Bridge Functionality Outline • Overview • Ethernet Switches and Bridges • Frame Transmission Modes • How Switches and Bridges Learn Source MAC Addresses • How Switches and Bridges Forward and Filter Frames • Summary PROPRIETARY 1 Ethernet Switches and Bridges • Address learning • Forwarding the filtering decisions • Loop avoidance PROPRIETARY Frame Transmission Modes Cut-Through • Switch checks destination address and immediately begins forwarding frame Store and Forward • Complete frame is received and checked before forwarding Fragment-Free • Switch checks the first 64 bytes, then immediately begins forwarding frame PROPRIETARY 3 MAC Address Table • The initial MAC address table is empty. PROPRIETARY 4 Learning Addresses • Station A sends a frame to station C. • The switch caches the MAC address of station A to port E0 by learning the source address of data frames. • The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded). PROPRIETARY 5 Learning Addresses (cont.) • Station D sends a frame to station C. • The switch caches the MAC address of station D to port E3 by learning the source address of data frames. • The frame from station D to station C is flooded out to all ports except port E3 (unknown unicasts are flooded). PROPRIETARY 6 Filtering Frames • Station A sends a frame to station C. • The destination is known; the frame is not flooded. PROPRIETARY 7 Filtering Frames (cont.) • Station A sends a frame to station B. • The switch has the address for station B in the MAC address table. PROPRIETARY 8 Broadcast and Multicast Frames • Station D sends a broadcast or multicast frame. • Broadcast and multicast frames are flooded to all ports other than the originating port. PROPRIETARY 9 Summary • Ethernet switches and bridges increase the available bandwidth of a network by creating dedicated network segments and interconnecting the segments. • Switches and bridges use one of three operating modes to transmit frames: store and forward, cut-through and fragment-free. • Switches and bridges maintain a MAC address table to store address-to-port mappings so that they can determine the locations of connected devices. • When a frame arrives with a known destination address, the frame is forwarded only on the specific port connected to the destination station. PROPRIETARY 10 Sixnet, LLC 331 Ushers Road Ballston Lake, NY 12019 T +1 518 877 5173 F +1 518 877 8346 [email protected] www.sixnet.com