To start with, let’s define our terms:

So that seems pretty cut and dry, but which one is better? That all depends on what you mean by better. Let’s take a look at the benefits and drawbacks of each. First, the benefits and drawbacks of custom silicon:

Now let’s take a look at the benefits and drawbacks of merchant silicon:

Arista uses merchant silicon exclusively for all of the reasons listed, but what about the drawbacks? The two drawbacks I listed for merchant silicon seem pretty severe to me, especially the one about there being no competitive advantage. I mean, isn’t that why people buy one brand of switch over another, for the competitive advantages?

When I say there’s no competitive advantage, I mean that there is no competitive advantage to using that ASIC compared to another vendor using that ASIC. There are a couple of things to take into consideration with that statement. Let’s take a look at the Arista 7050S-64 as an example. It uses the Broadcom Trident+ ASIC to deliver 64 ports of 10 Gbps non-blocking goodness in a 1 rack unit box. Many other vendors, as of May 2012, offer similar switches that use the Broadcom Trident+. Arista’s advantage in this space is that they have very efficient, modular, and portable hardware designs, and when a newer ASIC such as the Trident+ comes out, they can incorporate it into new products quickly. Other vendors might very well have the same ability, so this advantage might be small or fleeting, but it exists nonetheless. Remember, too, that how a vendor implements an ASIC can have a tremendous advantage. This is one of the areas where Arista shines.

Another issue is the idea that no proprietary features are possible, and that’s true, so far as the ASIC hardware is concerned. Arista overcomes this limitation by differentiating themselves with their Extensible Operating System (EOS). Much of this book is dedicated to the features of EOS, so I won’t go into them here, but suffice to say, EOS gives a significant competitive advantage to Arista that, so far as I’ve seen, can’t be matched by any other vendor, at least not yet.

Proprietary features can be a good thing, but they can limit the ability to expand a network using different vendors and, in some cases, cause designs to be so tightly integrated into a single vendor as to cause severe limitations in the future. This limitation, commonly called vendor lock, can be a real problem when it comes time to upgrade the network.

Perhaps the most compelling argument for the success of merchant silicon–based switches is that some of the biggest proponents of custom silicon have released merchant silicon switches. Cisco’s Nexus 3000 switches all use Broadcom Trident ASICs. And why wouldn’t they? If the Trident ASIC is an advantage for Arista, and anyone can buy them from Broadcom, then Cisco has every right to build the best switch they can, using the same hardware. It’s up to you to decide if Cisco’s NX-OS is a better choice than Arista’s EOS.

EOS offers the ability to show what ASIC is installed in your switch. To see the ASIC in use, use the show platform ? command. Here’s the output from a 7124SX:

Arista-7124#sho platform ?
  fm4000  fm4000 chip

Here’s the output from a 7050S-64:

Arista-7050#sho platform ?
  trident  Trident chip

The choices offered by each switch are different, depending on the ASIC installed. Here are the options for the 7124SX:

Arista-7124#sho platform fm4000 ?
  bali1                     bali1 switch
  interface                 Show interface-specific info
  mac-address-table         hardware MAC address table
  mac-flush-request-status  Show internal MAC flushing status
  mirror-groups             Show internal mirror session info

And here are the options presented on a 7050S-64:

Arista-7050#sho platform trident ?
  counters           Trident debug counters
  interface          Show internal interface state
  mac-address-table  Show hardware MAC address table
  mmu                Trident MMU information
  mroutes            Show internal multicast routes
  routes             Show internal routes
  tcam               Trident TCAM information

If you can get your hands on an Arista switch, I encourage you to dig around in these commands, because there is some really useful information in there. Table 3-1 is a list of the ASIC types for each Arista switch, as of May 2012.

Certain ASICs provide certain features. For example, the LANZ feature is only available on Arista 712X switches due to the FM4000 ASICs they incorporate. Since the 7050S-64 does not use the FM4000 ASIC, the switch does not support LANZ.

In your day-to-day network operation duties, do you care what ASICs are in your switches? Probably not. Still, it pays to know what you’re talking about when the vendors come a-courting.

It’s also important to consider what sort of power we’re talking about here. Consider this: the Arista 7050S-64 supports 64 10 Gbps non-blocking Ethernet ports in a 1 rack unit (RU) switch, using one ASIC. The admittedly aging Cisco 6509 supports only 28 10 Gbps non-blocking Ethernet ports, and that’s in a full 15RUs, consuming much more power and producing much more heat. It also uses a lot more than one ASIC to do it, which is one of the reasons that these big switches consume more power and generate more heat. The 6509 is capable of many more enterprise features and is almost infinitely more expandable than the Arista 7050S-64, so it’s not a strictly apples-to-apples comparison. Unless all you need is non-blocking 10 Gbps port density, in which case the Arista 1RU switch wins handily.

The Cisco 6509 is a great switch, and I’m not knocking it here. It is, however, a great example of the long product cycle induced by the custom silicon mindset. Though it supports high-density 10 Gbps blades, with only 40 Gbps available in each slot (using Sup 720s), those blades are highly oversubscribed. It’s been around for a long time though.

There is one more potential benefit to merchant silicon, and that is the possible future of Software Defined Networks (SDN). Think of SDN as a cluster of switches, all controlled by a single software brain that is running outside of the physical switches. With such a design, the switches become nothing more than ASICs in a box that receive instructions from the master controller. In such an environment, the switch’s operating system would be much simpler, and the hardware would need to be commoditized so that any vendor’s switch could be added to the master controller with ease. Merchant silicon–based switches lend themselves to this type of design paradigm, whereas a custom silicon solution would likely only support a master controller from that switch’s vendor.

Will SDN become a widespread reality? I don’t know. I think the idea has merit, but as of mid-2012, I’m not making purchasing decisions based on it. That viewpoint may change in the next few years.

So, which is better: custom silicon, or merchant silicon? As far as Arista is concerned, merchant silicon is the path they’ve chosen. I can’t tell you which is better, because I’ve seen great products from both camps. I will tell you that I really like what I’m seeing as a result of the competition caused by vendors moving to merchant silicon. Take EOS, for example. I think it’s the best networking operating system I’ve ever seen. If that came to be as a result of using merchant silicon, then I’m a fan.