Shortest Path Bridging

Shortest Path Bridging (SPB), specified in the IEEE 802.1aq standard, is a computer networking technology intended to simplify the creation and configuration of networks, while enabling multipath routing.

It is the replacement for the older : IEEE 802.1D, IEEE 802.1w, IEEE 802.1s. These blocked any redundant paths that could result in a layer 2 loop, whereas SPB allows all paths to be active with multiple equal cost paths, provides much larger layer 2 topologies, supports faster convergence times, and improves the efficiency by allowing traffic to load share across all paths of a mesh network. It is designed to virtually eliminate human error during configuration and preserves the plug-and-play nature that established Ethernet as the de facto protocol at layer 2.

The technology provides logical Ethernet networks on native Ethernet infrastructures using a link state protocol to advertise both topology and logical network membership. Packets are encapsulated at the edge either in media access control-in-media access control (MAC-in-MAC) 802.1ah or tagged 802.1Q/802.1ad frames and transported only to other members of the logical network. Unicast, multicast, and broadcast are supported and all routing is on a symmetric shortest paths.

The control plane is based on the Intermediate System to Intermediate System (IS-IS), leveraging a small number of extensions defined in RFC 6329.

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