Shortest Path Bridging (SPB) ￼Layer 2 frame routing protocol developed by the IEEE as a new control plane for Q-in-Q and MAC-in-MAC.
* IEEE 802.1aq standard was eventually approved on March 29th, 2012 (seven years development with the last three years of continuous promises about delivery).
* Data plane uses L2 forwarding built on existing IEEE Ethernet and OAM features
* Backbone L2 frame encapsulates L2 payload frames using either SPBV or SPBM. SPBV for Enterprise and SPBM for Metro Ethernet/Service Provider use.
* SPBV – 802.1ad (PB/Q-in-Q)
* SPBM – 802.1ah (PBB/MAC-in-MAC)
* L2 protocol with no hop count, frames are unchanged during forwarding
* Control plane uses IS-IS
* Used for shortest path calculations
* Limited interest from vendors or operators to implement widely, major vendor support is now for TRILL
There is a good explanation of SPB from NANOG 49
You can find some information at IEEE 802.1a: Shortest Path Bridging (SPB) – but because the IEEE conducts all their work in secret you cannot see the final standard.
SPB has some promise for use in Metro Ethernet in Service Provider networks. However the cloud providers have moved towards L3 Overlays and Enterprise have moved into TRILL. TRILL has the same outcome as the SPM. This is mostly because the IEEE took so long to finalise the SPB standard.