Posted by: Shamus McGillicuddy
data center networks, Ethernet, IEEE, IETF, NANOG, Networking, shortest path bridging, TRILL
Is TRILL a “terrible idea?” Does Shortest Path Bridging rule? I have no clue.
TRILL (Transparent Interonnection of Lots of Links) and 802.1aq (AKA Shortest Path Bridging or SPB) are very similar standards from two different governing bodies – the IETF and IEEE, respectively. Both standards aim to replace spanning tree protocol, which has become inhibitory in advanced data center networks today. Both standards seek to expand Layer 2 Ethernet domains and to provide multipathing and resiliency capabilities that are just not possible with spanning tree.
Vendors and pundits often gloss over the intricate differences between the two standards, probably because most of us in the media lack the technical knowledge to grasp the finer points involved. Vendors are embracing one standard or the other and it remains to be seen what the consequences of this divergence will be.
It was with this in mind that I reviewed with great interest the the PDF slide deck for a panel discussion held at the NANOG50 meeting in Atlanta last October, “The Great Debate: TRILL versus 802.1aq (SPB),” After reading through the slides, I really wish I was there for this talk.
The first 50 slides consist of a extremely technical exploration of the competing standards. After that, the slides move into a head-to-head comparison between the two standards, with advocates of each standard giving their own version of the history behind how we got to this point. In slides that appear to be attributed to Donald E. Eastlake III, co-chair of the IETF TRILL working group, things appear to get a little contentious.
Slide 57 describes how Dr. Radia Perlman, inventor of spanning tree protocol (STP), proposed the idea for TRILL to the IEEE 802.1 working group originally. The idea was rejected because the working group didn’t see a problem with STP. The slide claims that the working group thought TRILL was a “terrible idea,” that the idea of routing in Layer 2 “sucks” and that hop counts are “evil.”
After that, Perlman brought her proposal to the IETF, which embraced the idea and started its own working group. Meanwhile, the 802.1 group eventually recognized that STP did present some problems to the evolving data center industry, and so it launched SPB (802.1aq). The slides claims that the 802.1aq working group originally started out trying to build a replacement for STP that took an approach that differed from TRILL, but gradually SPB evolved into something that looks extremely similar to TRILL.
In subsequent slides that present the IEEE view, but whose specific attribution is unclear, the 802.1aq point of view is that TRILL will require new hardware and a new Ethernet OAM (Operations, Administration and Maintenance) standard. Shortest Path Bridging, on the other hand, can use existing Ethernet ASICs.
I wonder what the tone of this talk was like. Were the disagreements friendly and tongue-in-cheek, or are there really hard feelings on this issue? Perhaps we would have found out in the question and answer period at the end of the talk. The first question posed on slide 64 reads: “Why can’t the IEEE and IETF work together and finalize one solution?”
It’s a good question. Perhaps it will all be rendered moot by the market, as vendors decide which standard has real traction.