JUNOS High Availability

Redundancy and the Layered Model

Because most corporations have come to rely on data communications as a means of generating profit, we can safely assume that the simple design shown in Figure 1-1, with its complete lack of fault tolerance, is inadequate for the majority of corporate needs. Redundancy is necessary, so we must redesign the simple transport network.

Redundant network architectures fall into one of four basic categories:

Redundant site architectures

Rely on identical systems and services, placed in geographically disparate locations, to support enterprise-level redundancy.

Redundant system architectures

Rely on paired groupings of systems (routers, switches, servers) to provide service resiliency when chassis or components fail.

Redundant component architectures

Rely on additional interface cards, processor boards, power supplies, and other major components within individual chassis to provide chassis resiliency when components fail.

Hybrid redundancy schemes

Use a combination of system, component, and site redundancy elements to provide resilient services. This is by far the most common category.

Redundant Site Architectures

Figure 1-2 shows the simple network design from Figure 1-1 replicated at a site that is geographically distant from the primary site. The advantage of having the same architecture at two different sites is that it provides resilient routing of traffic during system or component failure, as well as during catastrophic disasters at the primary site. Also, ...