TRILL (TRansparent Interconnect of Lots of Links) is considered by some to be the heir-apparent to spanning-tree’s throne. After all, Radia Perlman was the force behind STP, and her name heads the list of authors for RFC 6325, the base TRILL protocol specification. For that reason alone, it seems a natural progression to move from STP into TRILL, but that’s not what we see happening, at least not yet. Instead, we see a hodge-podge of alternate solutions to the same problem, that of maximizing connected swaths of data center while minimizing hops and associated latency, maintaining a loop-free topology, and not wasting any links in the process.
The roster of technologies that obviate (or at least reduce) the need for TRILL is lengthy, with many groups representing vendors and standard bodies offering various approaches. For example…
- Multichassis etherchannel. Spreading an LACP link across two switches does allow for forwarding on all interswitch links, but it’s not a topological “any-any”. In addition, vendors’ MEC solutions are not interoperable. You can’t take an Arista switch, mate it to a Cisco switch, and present a unified MEC uplink to an adjacent node. Examples of MEC include Cisco’s Nexus virtual port channel (vPC) and Arista’s multichassis link aggregation (MLAG).
- Shortest path bridging. SPB is the IEEE’s answer to IETF’s TRILL, and is seeing some backing from vendors like Avaya and HP. Similar to TRILL in that it uses a routing protocol at layer 2 to calculate a forwarding path, SPB is also experiencing slow adoption.
- Intelligent Resilient Framework. Built upon a stacking technology, HP’s IRF allows up to four (last I knew) A12500, A10500, A9500, A7500, A58XX, or A55XX switches to act as a single logical switch.
- Virtual Switch System. Cisco’s VSS with properly equipped Catalyst 6500s allows a pair of the big Cats to act as a single logical switch.
- Virtual Chassis. Up to 10 of Juniper’s EX4200 line of switches can be connected in various physical combinations via dedicated links.
- QFabric. Juniper’s data center beast is a proprietary method of building an any-to-any topology using ToR switches meshed through a central fabric interconnect and managed via an external control plane.
- OpenFlow. OpenFlow-capable switches can be used to build a complex data center topology centrally managed by a controller that programs forwarding tables as directed by an application. Still developing, OpenFlow is looked at askance by data center designers who observe that OpenFlow is not actually open source in the strictest sense, and might fairly consider OF as a corner case solution. Although Google’s recent revelation of their wide OF deployment was a notable success for the fledgling protocol, that was perhaps the ultimate corner case. OF will likely see more traction as vendors begin building holistic solutions that leverage OF as a part of an overall networking solution.
While hardly a comprehensive list of the alternate topology technologies there are to choose from today, even this quick look shows that there’s a whole lot of competing protocols out there seeking mind share. And wallet share. So where does that leave TRILL?
Cisco is probably best positioned to drive market adoption of TRILL, and they are certainly a big TRILL player with FabricPath. However, Tasman Drive is currently positioning FabricPath as a play for big data centers, as opposed to the STP-alternative everyone should embrace. FabricPath is a licensed feature of the Nexus product line, and as such isn’t seeing a groundswell of implementations among the significant numbers of small and mid-level shops that are deploying Nexus to gain 10GbE density.
Brocade is also leveraging TRILL, basing much of their VCS Ethernet fabric technology on the specification, but Brocade does not command enough share of the ethernet switching market to drive wide adoption. Notable is that both Cisco and Brocade’s TRILL implementations are pre-standard (read: proprietary). It’s taken so very long for the TRILL standard to settle, that it’s been a moving target for vendors to code into their gear.
Other vendors including Dell, HP, IBM, Extreme, and Huawei have made noises in a TRILL-direction for 2012. “Why so long for other vendors to offer TRILL?” you might wonder. That’s a fair question, and the answer (at least in part) is that TRILL means new hardware. TRILL is an encapsulation technology, so to cram a TRILL frame through the silicon you need…well…different silicon. Broadcom’s BCM56840 series chipset can handle TRILL (as well as SPB), and so vendors deploying merchant-silicon based switches are potentially ready to move ahead in the coming months.
The question still remains. Does TRILL stand a chance against all of these other competing technologies? Time will tell, but from where I sit, the customers are going to need to want it. But until some technologies prove themselves as contenders or fall by the wayside, it’s tough to pick a winner. And no one with the title of “architect” or “director” wants to back a loser.