Domains and Hierarchical Network Design
One for the first questions you need to ask is “Where should I put the L1/L2 borders in a network?” In other words, how do IS-IS domains overlay onto a network's hierarchical structure? Of course, before answering this question, we need to ask yet another—what sort of hierarchy is the network built on? Figure 4-1 illustrates the two most common types.
Figure 4-1. Two models of hierarchical networks
Traditionally, hierarchical network designs have three layers of intermediate systems: the core, distribution, and access layers. Each of these layers serves a specific purpose in the network, splitting network ...