Arista touts next-gen switch as malleable as a T-1000 Terminator
Plunder me x86, programmable pipeline, and OpenFlow booty
Nobody has had his fingers in so much of the data centre pie as Andy Bechtolsheim, founder of Sun Microsystems, Granite Systems, Kealia, and Arista Networks. When Bechtolsheim and his team of techies at Arista say they have come up with their own way of doing software-defined networks (SDN) with their switches, people will stop and listen. Well, if they are smart, anyway.
With all software-defined networks, you want to break the control plane that manages switch and routing tables from the forwarding plane that actually does all that work. With many OpenFlow designs, explains Martin Hull, senior product manager at Arista, those tables are changeable, but they are also moved out of the switching devices themselves and plunked onto an OpenFlow controller.
That controller can see what is going on in the network and shape the traffic across the switches and routers in real time to changing conditions, like a Terminator robot reshaping into a new form. This is all well and good, and Hull is very careful to not say this introduces a single point of failure in OpenFlow networks. But it does mean you need to worry about the resiliency of that OpenFlow controller and all of the control plane eggs it has in its basket.
Arista says having an OpenFlow controller is a great thing, but it also says that it wants to keep a resident and resilient control plane on the switches, in this case running on the dual-core x86 Linux server embedded in the switch. This server has 2GB of memory and 2GB of flash memory and can run user applications inside virtual machine partitions, and it has been embedded in all Arista switches since the company's first products came out three years ago . In fact, Arista wants companies to go with a hybrid model, with multiple and redundant OpenFlow controllers and flexible hardware-based forwarding in the switches. And the 7150S switch announced today embodies these ideas.
The real issue, says Hull, is that it takes too long for new protocols to be implemented because they are often tied very tightly to specific custom chips (ASICs) in the switches. So what Arista has created is a switch dog that can be taught new tricks as it gets old.
The 7150S switch is based on Intel's hot-out-of-the-oven FM6000 "Alta" ASIC, which was announced in November 2010  and expected in the second quarter of last year. It took a little longer for the FM6000 chip to come to market in the wake of Intel buying Fulcrum Microsystems back in July 2011 . Only last week at Intel Developer Forum, Chipzilla was showing off a reference design switch  called "SeaCliff Trail" based on the Alta chip, its Core processors and a Linux software stack from its Wind River software unit. This SeaCliff Trail reference platform looks a bit, in concept, like what Arista has cooked up. The big difference is Intel has a reference architecture for SDN, and Arista has a product you can buy today.
The Alta ASIC supports OpenFlow 1.0 control protocols and VXLAN, the extended LAN virtualization protocol espoused by VMware that puts a layer-2 overlay on top of layer-3 networks so virtual network links don't break as virtual machines flit across data centres. The Fulcrum chip also supports the NVGRE alternative that Microsoft, Intel, Dell, and Hewlett-Packard have offered, but for whatever reason, Arista is not supporting NVGRE yet. But, as Hull says, it can be added in a flash (quite literally) whenever Arista wants to do it.
The malleable Arista 7150S 10GE/40GE switches
Like other Arista switches, the 7150S runs Arista's own Extensible Operating System, or EOS, which is a network operating system based on the Linux kernel. The box does not have a Altera Stratix V field programmable gate array (FPGA) accelerator to emulate various kinds of hardware or to run very specific algorithms right in the network flow, as does the Arista 7124FX. The 7150S instead has a programmable pipeline in the ASIC that allows for firmware in the switch to be altered to support new or improved protocols as necessary.
The 7150S has a maximum of 64 ports, which is the limit of the FM6000 chip used by Arista, and that is better than the 24-port upper limit on the "Bali" FM4000 chip from Intel/Fulcrum used in prior Arista switches. That FM6000 ASIC sports 1.28Tb/sec of switching bandwidth, can handle 960 million packets per second forwarding and does L2 and L3 forwarding at wire speed. The port-to-port latency is the same regardless of whether you are doing it from L2 or L3 of the network or almost regardless of port count on the switch or packet size. As you can see below, as you add ports, you add a little latency, but as packet sizes grow or shrink, the latency is pretty rock solid:
Latency profile for 10GE ports on the 7150S switch
For the 24-port variant, the port-to-port latency runs around 360 nanoseconds, compared to just under 500 nanoseconds for the prior Bali FM4000 switch ASIC, which topped out at 24 ports, 480Gb/sec of bandwidth, and could handle 360 million packets per second. (This Bali chip was used in the Arista 7124SX switch, announced in March , among many other devices across various switch makers.) The 7150S has 64KB L2 table sizes and 84KB L3 table sizes for unicast and 36KB L2 and 23KB L3 tables for multicast, which are big enough to be useful for very large networks, according to Hull. The 7150S switch also includes Network Address Translation (NAT) support, and can do line-rate NAT at under 1 microsecond, which means it can be used in many instances instead of more expensive modular switches, which pack NAT unlike fixed-port boxes. (Well, until now. But don't tell the modular switch salesperson at Arista that.)
Like many switch makers today, Arista sells splitter cables that let companies split 40GE ports down into four 10GE ports if they want to buy a model with faster uplinks and split them into more and slower uplinks and downlinks today and use them for aggregation later. What is new with the AgilePorts that Arista is selling with the 7150S machine is that companies can now go the other way, ganging up four 10GE ports with a merger cable that turns it into a 40GE port.
There are three models of the 7150S switch. The 7150S-24 has two dozen 10GE ports, and it is available today for $12,995, or around $541 per port. The 7150S-52 has 52 10GE ports, as the name suggests, while the 7150S-64 has 48 10GE ports and four 40GE ports that can be split down to 16 additional 10GE ports (and hence the 64 portness of the box). The latter two models will ship in the fourth quarter and will be priced at a similar $500-per-port range. ®