Tech Notes: What is Shortest Path Bridging IEEE 802.1aq – Brief

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.

  • Auto Test

    I have heard that TRILL has problems with multicast??

  • David Allan

    Hmmm, no information here that has not been debunked before….IEEE is not really in secret, inputs to the discussion are publically available, and there still has not been a TRILL interop, just a bunch of proprietary implementations claiming a blanket term to get IETF “cachet”. So it is a marketing term, not a technology.

  • János Farkas

    Hi Greg,

    IEEE 802.1 is an open SDO, nothing is done in secret. Anyone
    can attend the meetings (
    after paying the registration fee, which is the common practice in case of conferences and standards meetings. The e-mail archive and the draft standards are available at so as the comments submitted to the drafts and their resolution. Furthermore, changes are illustrated in the drafts. Everything is open and backtrackable, nothing can be done hidden or in secret. (There is a very basic access control for ongoing work protected by the most well-known password of the universe. The access is free of charge, contact 802.1 people if you would like to contribute.)

    The IEEE 802.1 aq Shortest Path Bridging standard is available free of charge at, just like any other 802.1 standard today: For more detailed references, you may refer to the 802.1 tutorial given at the last IETF:

    Best regards,

  • Guido

    Hi all,

    I fully agree with János and David. Work in the IEEE Standards Association (SA) is not secret. Anyone can participate. For a limited period of six month after ratification a standard is available to the members of the Working Group (WG) and through the IEEE-SA’s webshop only. Afterwards, standards are available free of charge through Get-IEEE 802 program.

    I admit that work in IETF is a little bit “more open” but that is really marginally and relates only to the necessary login that IEEE-SA requires.

    Best regards,


    • Etherealmind

      My opinion remains unchanged. The IEEE is a pain in my posterior and should have the Ethernet standard taken somewhere that actually gets stuff done. The IEEE process remains a quasi-secret cabal of people who would rather navel gaze than deliver on their promises.

      We need better standards organisation than the IEEE.