While I was at Brocade Tech Day, I had the wonderful opportunity to sit down with Jon Hudson (@the_solutioneer) and just talk for about half an hour. While the rest of the day was a whirlwind of presentations and interviews, Jon and I talked about all manner of things not related to VDX or VCS. Instead, we had a very fascinating discussion about TRILL and SPB.
For those not familiar, TRILL is the IETF standard for the issue of layer 2 multipath. It’s a very elegant solution for the spanning tree problem. Our data centers today are running at half capacity. That’s not because we don’t have enough bandwidth, though. It’s because half our links are shut down, waiting for a link failure. Thanks to 802.1d spanning tree, we can’t run two links at the same time unless they are bundled into a link aggregation (LAG) solution. And heaven forbid we want to terminate that LAG bundle on two different switches to prevent single-switch failure from affecting our traffic. Transparent Interconnection of Lots of Links (TRILL) fixes this by creating a layer 2 network with link state. It accomplishes this by running a form of IS-IS, which allows the layer 2 nodes to create an SPF table and determine not only the best path to a node, but other paths that could be equally as good. This means that we have a real fabric of interconnections with no blocked links.
802.1aq Shortest Path Bridging, or SPB informally, is the IEEE version of a layer 2 multipathing replacement for spanning tree. It looks a lot like TRILL and even uses IS-IS for the layer 2 protocol as well. It does differ in some respects, such as using MAC-in-MAC encapsulation for frames as opposed to rewriting the header like TRILL does. This makes it very attractive to the service provider market, as they don’t have to buy a bunch of new gear to get everything up and running quickly on SPB. Looking at the proponents of SPB, such as Avaya and Alcatel-Lucent that really comes as no surprise. Those companies are heavily invested in the service provider space and would really love to see SPB adoption take off as it would protect their initial investments.
The showdown between TRILL and SPB isn’t that far removed from the old showdown between VHS and Betamax. For those not entirely familiar, this was a case of two competing standards that was eventually settled in the court of the consumer. While many regard the early Betamax units as technologically superior, there was an issue of tape length (1 hour vs the VHS 2 hour limit). As time wore on, there was significant development done on both sides that stretched the formats to their absolute limits. However, by the end, VHS had won due to simple popularity. Since VHS had become the most popular format for consumers, even the supposed superiority of Betamax couldn’t save it from being relegated to the junk pile of history. Another more recent case is the battle between HD-DVD and Blu-ray. Similarly to the analog format wars decades earlier, the digital disc war erupted from two alliances thinking they had the best solution to the problem. Blu-ray eventually won out in much the same way that VHS – by becoming the format that most people wanted to use. The irony that Sony actually won a format war isn’t lost on a lot of people either.
I believe that we’re going to see something like these showdowns in TRILL vs. SPB. Right now, the battle lines seem drawn between the data center vendors supporting TRILL and the service provider vendors getting ready to implement SPB. Whether or not one of the solutions is technically superior to the other is inconsequential at this point. It’s all going to come down to popularity. Brocade and Cisco have non-standard TRILL implementations in VCS and FabricPath. The assumption is that they will be compatible with TRILL when a working solution is finally released. I’m also guessing that we’re going to see more support for TRILL in the cloud providers to maximize their revenue potential by offering non-blocking paths to increase throughput for those hungry cloud applications. Brocade showcased some providers moving to VCS at Brocade Tech Day. If that’s the case, we’re going to see TRILL at the enterprise level and the cloud provider level connected by an SP core running SPB. Just like Betamax being the favorite of the professional video industry, SPB will be the go-to protocol for providers, as they can put of yet one more round of equipment upgrades. I think by that point, however, TRILL will have obtained enough critical mass to drive adoption to the point where TRILL silicon will be a very inexpensive option on most new equipment in a few years, perhaps even becoming the default configuration. If that is indeed the case, then TRILL will indeed become the VHS or Blu-ray of this protocol war.
I can still remember going into the video store and seeing the great divide. On one side, Betamax. On the other, VHS. Slowly, the Betamax side of the house shrank away to nothing. It happened again with HD DVD and Blu-ray. In the end, both format wars came down to popularity. VHS was in more households and offered the ability to record two hours worth of programming instead of one. Blu-ray got the popular movie studios on board quickly, like Disney. Once the top selling movies were on Blu-ray, the outcome was all but guaranteed. In the big debate of TRILL against SPB, it’s going to come down to popularity. I think we’re already seeing the beginning of TRILL winning this fight. Sure, the service providers are going to use SPB as long as they can to avoid upgrading to TRILL-compatible hardware. I could even make a pretty compelling case the neither of these two layer 2 protocols would make a bunch of sense for a service provider. At the end of the day, though, I’m pretty sure that we’ll eventually be speaking about SPB in the same hushed nostalgia we reserve for the losers of the format wars so many years ago.
Here are a few posts about TRILL and SPB that generated some ideas for me. You should check them out too:
Does TRILL Stand A Chance At Wide Adoption – Ethan Banks
Why SPB Doesn’t Get Any Attention – Greg Ferro
TRILL and 802.1aq (SPB) Are Like Apples and Oranges – Ivan Pepelnjak
NANOG 50 TRILL vs. SPB Great Debate – PDF of a huge discussion presentation