Layer 2 Oriented Designs Fail at Internet Scale

by Jeff Loughridge

This post’s title summarizes a tenet of designing large IP networks. Layer 3 networks have numerous advantages in efficient use of available paths, troubleshooting (think visibility), and fault domain containment to name a few.

The tech industry’s market leaders offer evidence of Layer 3’s superior scaling properties. The world’s largest ISPs use Layer 3 oriented designs as do content providers Google and Facebook. Amazon’s AWS, the undisputed leader of public cloud providers, is built on Layer 3. Wonder why you can’t get broadcast or multicast in your EC2 instance? Now you know.

Layer 2 still has too much focus in the network designs of several segments of the industry. The mobile broadband providers–with their history of walled-garden environments–will need to re-architect their networks on a Layer 3 foundation. Keeping up with the massive influx of bandwidth (at ~$50 USD/month per subscriber!) forces this change. These Layer 2 relics contribute negatively to the cost per bit and customer satisfaction.

Layer 2 oriented designs are also dominant in corporate data centers and corporate networks in general. I’ve probably heard every reason why the Layer 2 focus is necessary. I’d argue that over 90 percent of Layer 2 requirements stem from old assumptions about building corporate IT infrastructure. Of course, overhauling these networks is non-trivial, and I don’t underestimate the massive effort required. But it can be done. An excellent 2008 Network World article called The Google-ization of Bechtel describes Bechtel’s IT revamp. If Bechtel can fundamentally change its IT architecture, why can’t your organization?

Before investing in hacks to make Layer 2 scale, consider how a Layer 3 oriented design can reduce outages, simplify new service introduction, and scale existing services to meet business needs.

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