A regional anycast is an improvement on the basic model. It’s best suited for worldwide networks, including global CDNs.
With regional anycast, a network is divided into virtual clusters; each corresponds to a specific geographic area. Identical IP ranges are advertised only on nodes within the region, not on the rest of the network.
Cluster topology offers control over routing choices of local ISPs. By limiting the number of options, local ISPs must route traffic to a nearby node, even if compelled to do otherwise by suboptimal configurations or spur of the moment decisions.
Today, most commercial CDNs rely on regional anycast to further accelerate their content delivery.
Internet service providers are classified into three tiers based on their connection and payment agreements.
Tier 1 providers are a select group of carriers representing the Internet backbone. A typical tier 1 ISP operates its own networks and doesn’t pay for bandwidth usage. It also maintains interconnected (peering) relationships with other tier 1 ISPs.
Second and third tier providers are smaller carriers who purchase IP transit from a tier 1 ISP and resell it to their users. A typical tier 2 provider is a local carrier with some peering arrangements. Tier 3 providers constitute even smaller ISPs, or dedicated networks (e.g., one belonging to a university).
Of the three groups, tier 1 providers offer the best network performance by far. They have more presence, better peering arrangements, and direct control over traffic flow.
In addition, many tier 1 networks have global coverage. This allows effective end-to-end routing of both transnational and intercontinental traffic.
Commercial CDNs use their funds and bargaining power to purchase transit directly from tier 1 providers. As a CDN subscriber, your website visitors benefit from that arrangement. They reach your website directly via the Internet backbone, with minimal hops and very low risk of packet loss.
Much focus is given to CDN caching and FEO features, but it’s direct tier 1 network access that often provides the largest performance gains. It can revolutionize your website page load speeds and response times, especially if you’re catering to a global audience.
Almost exclusively, tier 1 providers peer with other tier 1 providers for two practical reasons:
“The Tier 1 Club” is the result. Here top-tier ISPs engage in donut peering—exchanging transit solely between themselves for the benefit of their direct users.
When using a CDN service that purchases tier 1-provided transit, you also benefit from the peering arrangements forged between these top-tier carriers.