The Network Hub

Jan 28 2011   4:51PM GMT

TRILL versus Shortest Path Bridging: Hard feelings?

Shamus McGillicuddy Shamus McGillicuddy Profile: Shamus McGillicuddy

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.

4  Comments on this Post

 
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  • Greg Ferro
    As I understand it, the market is heading down the path of TRILL for data centre, and SPB will be used by carriers / telcos with various opimisations that suit WANs. Of course, the fact that carriers don't HAVE to upgrade old equipment and make more short term profit wouldn't have anything to do with their choice of SPB.
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  • Reeegman
    The Site Expert Greg Ferro makes some interesting comments. Regarding on where the "market is heading". What can you share with us that leads you to believe the market is heading down the TRILL path? I understand that TRILL and SPB are standards being developed and yet to be completely ratified, for the enterprise space. So I am not sure where the carrier space comes in to play here. That is for a totally seperate discussion. Looking at the Great Debate White Paper, I see a number of items, that shed light on each technology. It is important that as enterprises begin the process of selecting a protocol for virtualizing the network, they should consider how simple this protocol will be required to implement and support. How comprehensive are the tools for troubleshooting? Are these tools interoperable between multiple vendors? How far can they extend this protocol cost effectiviely. Being able to extend this protocol from core to network edge will have very good advantages. How flexible will the deployment be? Will the technoiogy support the topologies that we have become accustomed to? Are we restricted as to where we can route? Can the technoloogy deliver informaton between points in a multipath fashion? Cost, flexibility, reliability should be driving the market. Hopefully.
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  • Gibanezfer
    I agree with Ferro and Reeeqman. Furthermore, simplicity is key to performance and maneagability. Among the multiple lessons to learn from Ethernet success one is "do not touch the Ethernet frame format". Link state at layer two, specially for ECMP, is far from simple. At the time these standards started discussion, it seemed that no alternative to link state existed. This is not the situation anymore. Our research approach is to look for extreme simplicity and architectural coherence with the bridging model and mechanisms (learning, filtering and forwarding) by just evolving them instead of hybridizing with routing. Here is (as recently uploaded to 802.1), just an example of a simple, implemented, shortest path bridge with native load distribution: [A href="http://www.ieee802.org/1/files/public/docs2011/fyi-ibanez-arp-path-0111-v03.pdf"] The last slide contains references to papers for detailed information. Comments wellcome.
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  • Peterashwoodsmith
    Shamus, Just spotted your post and thought I'd add a few 'first person' notes from the front lines which I've embedded inline below. > Is TRILL a “terrible idea?” Does Shortest Path Bridging rule? I have no clue. All protocols are compromises and standards based ones especially so. They both have aspects which I personally consider 'terrible' ;) One of my first rules of protocol and network design however is never to love or hate a protocol. Just use what works at the cost points you require. Unfortunatley that does not make for very exciting blog posts. > 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. The two most important differences are how packets are forwarded and how OA&M works. The IEEE solution fires packets like a rifle, targetting a very specific path while the IETF solution is more like a shot-gun. For OA&M the IEEE solution re-uses 802.1ag and Y.1731 .. for better or worse, while the IETF solution prefers something new , for better or worse. The IEEE forwarding solution will offer better control and runs on many current boards/asics while the IETF solution will offer better spread when hop counts get above 4 or so. Its a bit like comparing MPLS (802.1aq) to IP (TRILL) forwarding. Talking with customers we find some that don't want control and want the network to be totally transparent, others demand control. For example the customer I spent all afternoon with today was delighted in the symmetry and positively hate trying to debug 1/2 failed connections. Therefore to address all customers will require both forwarding modes in one protocol, or both protocols. Intelligent vendors will listen to their diverse customer requirements and not fall in love or hate one or the other method. Some customers don't mind spending money on new 40G cards if the cost brings them a new value while others naturally want to squeeze the maximum out of their investments, seems very reasonable to me. > After reading through the slides, I really wish I was there for this talk. It was recorded. There is a link at the bottom of the 802.1aq wikipedia link here: http://en.wikipedia.org/wiki/IEEE_802.1aq which shows the Tutorial video recorded at Nanog and I'm pretty sure you can find the debate video linked in that same general NANOG directory. > 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? Unfortunatley it was not as friendly as it should have been. I did review it and make a note to not rise to the bait as quickly next time ;) but compared to some of the stuff I've seen around MPLS-TP (or the early MPLS v,s ATM debates) it was positively friendly ;) Regards Peter Ashwood-Smith (Huawei)
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