TMS zl Management and Configuration Guide ST.1.1.100226

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Routing
OSPF
Figure 9-10. OSPF Network with WAN as Area 0
If these routers are the only routers at the remote sites or if the remote sites
are quite small, you could leave the network undivided. (A general rule is that
an area should include fewer than 50 routers.) In this case, all networks would
be defined as part of Area 0. (See Figure 9-11.)
Figure 9-11. OSPF Network with One Area
When you configure a router to run OSPF, you should also consider the type
of network. WAN networks are point to point, which means that your router
will synchronize its database with its one neighbor. However, your router may
also be acting as a DR, BDR, or other member in the multicast LAN
environment.
Refer to Table 9-16 for a summary of how OSPF manages route exchanges and
what parameters you can configure for the protocol.