IEEE 802.1aq

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Shortest Path Bridging ( SPB ), specified in the IEEE 802.1aq standard, is a technology for computer networks to simplify the structure and configuration of networks while at the same time supporting multipath routing .

Presented as a draft in 2006 and confirmed by the IEEE in 2012, Shortest Path Bridging is the replacement for older spanning tree protocols ( IEEE 802.1D STP, IEEE 802.1w RSTP, IEEE 802.1s MSTP), which only allowed a single path to the root bridge and blocked any redundant path that could create a level 2 loop. SPB allows all paths with the same cost ( English Multiple Equal Cost Paths ) to activate, and supports much larger Layer 2 topologies (up to 16 million compared to 4096 VLANs ).

SPB also supports faster convergence times and improves the use of meshed topologies through increased bandwidth and redundancies between all components through the possibility of distributing the load of the data traffic over all paths of the meshed network. In order to increase the reliability in the access level, SPB can use mechanisms for link aggregation, such as B. standards-based IEEE 802.1AX or proprietary MC-LAG implementations can be combined.

The technology allows logical Ethernet networks on pure Ethernet infrastructures through the use of a link state protocol to announce both the topology and the logical affiliation to a network. When entering the SPB network, packets are either packed in MAC-in-MAC 802.1ah or as tagged 802.1Q / 802.1ad frames and are only transported to other participants in the logical network. Unicast , multicast and broadcast are supported, and all routing takes place on symmetrical shortest paths.

An alternative to Shortest Path Bridging according to IEEE802.1aq is the Transparent Interconnection of Lots of Links (TRILL) standard developed by the IETF , which, however, is only suitable for unicast connections.

The control level is based on the Intermediate System to Intermediate System (IS-IS) protocol , supplemented by a small number of extensions that are defined in RFC 6329 IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging .


  • David Allan, Nigel Bragg: 802.1aq Shortest Path Bridging Design and Evolution: The Architects' Perspective . John Wiley & Sons, 2012, ISBN 978-1-118-14866-2 .

Web links

Commons : IEEE 802.1aq  - collection of pictures, videos and audio files

Individual evidence

  1. ^ IEEE working group 802.1aq
  2. IEEE 802.1aq