Loop free frame forwarding in layer 2 switched networks that use meshed topologies to provision for link and path redundancy is a continuing challenge. The challenge is addressed through special protocols at layer 2 that build logical trees over the physically meshed topologies, along which frames can be forwarded. The first such protocol was based on the spanning tree. The spanning tree protocol (STP) had high convergence times subsequent to topology changes. Rapid STP and IETF RFC 5556 Transparent Interconnection of Lots of Links (TRILL) on Router Bridges (RBridges) were then developed to reduce the convergence times. RSTP cntinued to use the spanning tree while TRILL adopted link state routing to support a tree from every switch. TRILL introduces high processing complexity into layer 2 networks. In this article a new meshed tree algorithm (MTA) and a loop avoidance protocol based on the MTA, namely the meshed tree protocol (MTP) are discussed. The MTA allows constructing several overlapping trees from a single root switch. This speeds up convergence to link failures. The MTP proposes a simple numbering scheme to implement meshed trees – thus, the processing complexity is low. The specification for the MTP is currently an ongoing IEEE standard Project 1910.1. In this article the operational details of MTP are presented and its performance evaluated and compared with RSTP.
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