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6.4 | ![]() |
Configuring OSPF Over NBMA | |
6.4.2 | ![]() |
Full-mesh Frame Relay |
The different NBMA topologies must be
understood before selecting an OSPF configuration strategy for a Frame
Relay network, or legacy X.25 network. Fundamentally, two possible
physical topologies exist for Frame Relay networks.
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The following sections describe how to configure OSPF in both full-mesh and partial-mesh Frame Relay networks. Full-Mesh Frame Relay
For OSPF to work properly over a multiaccess full-mesh topology that does not support broadcasts, each OSPF neighbor addresses must be manually entered on each router, one at a time. The OSPF neighbor command tells a router about the IP addresses of its neighbors so that it can exchange routing information without multicasts. The following example illustrates how the neighbor command is used:
Specifying the neighbors for each router is not the only option to make OSPF work in this type of environment. The following section explains how configuring subinterfaces can eliminate the need for the neighbor command. Configuring Subinterfaces to Create
Point-to-Point Networks In Figure
A full-mesh topology offers numerous advantages, including maximum fault tolerance. Unfortunately, full-mesh topologies can get expensive because each PVC must be leased from a provider. An organization would have to lease 45 PVCs to support just ten fully meshed routers. If subinterfaces are used to create point-to-point networks, then the 45 IP subnets must also be allocated and managed, which is an additional expense.
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