A zone is a named set of routes. Every route belongs to a zone. A zone affects the forwarding behavior of its routes:
For example, Figure 32 depicts a set of servers connected by routes within a multi-hop zone, Z1. If a client sends a message to a global topic on server B, the servers forward the message to A, C, D and E (assuming there are subscribers at each of those servers). In contrast, if Z1 were a one-hop zone, B would forward the message to A, C and
D—but D would
not forward it E.
Figure 33 illustrates an enterprise with four servers:
The goal is to forward messages from B1 and B2 to both M and R. The routing graph seems to contain a
cycle—the path from B1 to M to B2 to R duplicates the route from B1 to R. However, since these routes belong to the one-hop zone Z2, it is impossible for messages to travel the longer path. Instead, this limitation results in the desired
result—forwarding from B1 to M and R, and from B2 to M and R.
Figure 34 illustrates an enterprise with one-hop zones connecting all the servers in each of several cities in a fully-connected graph. Zone TK connects all the servers in Tokyo; zone NY connects all the servers in New York; zone PA connects all the servers in Paris. In addition, the multi-hop zone WO connects one server in each city.