Cisco CCNA Study Guide - Router Alley

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CCNA Study Guide v2.62 – Aaron Balchunas 224 Configuring OSPF Network Types (continued) The default OSPF network type for Point-to-Multipoint Frame Relay is still Non-broadcast Multi-access Network (NBMA). However, OSPF supports an additional network type called Point-to-Multipoint, which will allow neighbor discovery to occur automatically. To configure: Router(config)# interface s0 Router(config-if)# encapsulation frame-relay Router(config)# interface s0.2 multipoint Router(config-if)# frame-relay map ip 10.1.1.1 101 broadcast Router(config-if)# ip ospf network point-to-multipoint Additionally, a non-broadcast parameter can be added to the ip ospf network command when specifying point-to-multipoint. Router(config)# interface s0 Router(config-if)# encapsulation frame-relay Router(config)# interface s0.2 multipoint Router(config-if)# frame-relay map ip 10.1.1.1 101 Router(config-if)# ip ospf network point-to-multipoint non-broadcast Router(config)# router ospf 1 Router(config-router)# neighbor 10.1.1.1 Notice the different in configuration. The frame-relay map command no longer has the broadcast parameter, as broadcasts and multicasts are not allowed on a non-broadcast network. Thus, in the OSPF router configuration, neighbors must again be manually specified. Traffic to those neighbors will be unicast instead of multicast. OSPF network types must be set identically on two “neighboring” routers, otherwise they will never form an adjacency. * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
CCNA Study Guide v2.62 – Aaron Balchunas 225 The OSPF Hierarchy OSPF is a hierarchical system that separates an Autonomous System into individual areas. OSPF traffic can either be intra-area (within one area), inter-area (between separate areas), or external (from another AS). OSPF routers build a Topology Database of all links within their area, and all routers within an area will have an identical topology database. Routing updates between these routers will only contain information about links local to their area. Limiting the topology database to include only the local area conserves bandwidth and reduces CPU loads. Area 0 is required for OSPF to function, and is considered the “Backbone” area. As a rule, all other areas must have a connection into Area 0, though this rule can be bypassed using virtual links (explained shortly). Area 0 is often referred to as the transit area to connect all other areas. OSPF routers can belong to multiple areas, and will thus contain separate Topology databases for each area. These routers are known as Area Border Routers (ABRs). Consider the above example. Three areas exist: Area 0, Area 1, and Area 2. Area 0, again, is the backbone area for this Autonomous System. Both Area 1 and Area 2 must directly connect to Area 0. Routers A and B belong fully to Area 1, while Routers E and F belong fully to Area 2. These are known as Internal Routers. Router C belongs to both Area 0 and Area 1. Thus, it is an ABR. Because it has an interface in Area 0, it can also be considered a Backbone Router. The same can be said for Router D, as it belongs to both Area 0 and Area 2. * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
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Cisco CCNA Study Guide - Router Alley

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