History Of Networking – Tony Przygienda – History of BIER

In this History of Networking episode Tony Przygienda joins us to discuss his involvement in the origins of BIER (Bit Index Explicit Replication). BIER is a new take on an old problem, the efficient forwarding of point-to-multipoint (multicast) traffic.


Tony Przygienda
Russ White
Donald Sharp

Outro Music:
Danger Storm Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0 License


One Comment

  1. Christian Martin
    May 14, 2018

    Hi Russ, Tony, and Donald,

    Excellent podcast and excellent summary of BIER! I just wanted to add a little historical color to the development of BIER. The very, very initial work on BIER started in January of 2013 as a way to extend Segment Routing principles to multicast (we called it M-SR at the time). The goal was to enumerate and distribute trees, just as SR enumerates and distributes SIDs. As it turns out, there are just far too many trees to enumerate in a graph of arbitrary size (O(n^n) in a graph with n nodes – see Cayley’s method), but the endpoints are usually fairly manageable (O(n)). The eureka moment came after a small meeting of the SR lead operator group in Berlin at IETF 87. In that meeting, which came after a few months of work trying to figure out how to do M-SR, we conceded that the only possibility was to carry an adjacency matrix in the packet as a routing vector for all trees. We already had mLDP, which had some nice properties, so we left it at that.

    The next day, Ice Wijnands and Greg Shepherd and I met to discuss the post mortem and Ice had this nagging suspicion that there was a better way. Ice had driven to the IETF and had to drive back to Leuven, and, along the ride back, he realized that if you leverage the adjacency matrix represented at each node in the form of a shortest path tree, you can reduce the forwarding state in each packet to just the “bit string” representing that active receivers (the last row vector in the adjacency matrix). The drafts (and patents) were created quickly thereafter, and BIER was officially born.

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