TMS zl Management and Configuration Guide ST.1.0.090213

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Routing
OSPF
■ The OSPF area for each directly connected network
One common topology for a network is a headquarters, defined as Area 0, that
connects to stub areas at one or more remote sites. In this topology, the
headquarters’ routers that connect to the remote sites are ABRs. The routers
at the remote sites are internal routers. If a router connects to a public or other
external network, such as an ISP, it is an ASBR. (See Figure 9-9.)
Figure 9-9. OSPF Network with Headquarters (HQ) as Area 0
Another topology for an OSPF network is a network backbone that connects
two or more sites, each of which is an area. Routers or routing switches at
each site would be the internal routers for that stub area. The routers that
provide the connections between the areas would be ABRs. These routers
would have one or more VLANs in Area 0 and one or more VLANs in the local
stub area. They would thus string stub areas together. Such a topology is best
suited for two or more remote sites of roughly equal complexity. (See Figure
9-10. Note that this figure simplifies the topology. In reality, each stub area
would have many more routers or routing switches than the ones shown in
the figure.)