Verify the OSPF Protocol
Purpose
For OSPF to run on a router in your network, you must include the interfaces that run OSPF at the [edit protocols ospf] hierarchy level and, for those interfaces, the family inet statement must be included at the [edit interfaces interface-name unit logical-unit-number] hierarchy level.
Figure 10 illustrates an example an OSPF autonomous system (AS) consisting of multiple areas and different types of OSPF routers.
The AS in Figure 10 is organized hierarchically around a backbone area, 0.0.0.0. Portions of the network are designated as separate areas: 0.0.0.1, 0.0.0.2, and 0.0.0.3. The backbone is the connecting point for all other areas, and each area must attach to the backbone in at least one location. OSPF is based on the concept of a link-state database in which each OSPF router attempts to form adjacencies with its OSPF neighbor. Once the adjacencies are in place, each router generates and floods LSAs into the network. The LSAs are placed into the link-state database on each router where the shortest path first (SPF) algorithm is calculated to find the best path to each end node in the network.
All non-backbone areas (0.0.0.1, 0.0.0.2, and 0.0.0.3) contain routers internal to that area (R1, R5, and R6) as well as a single area border router (ABR) (R2, R3, and R4). Internal routers generate LSAs within their area. The ABR translates these internal LSAs into summary LSAs that represent the LSAs within its non-backbone area and floods the summary LSAs to the backbone. The ABR is also responsible for generating summary LSAs that represent the backbone LSAs and injecting them into its attached areas. Because the ABR belongs to more than one area, it maintains a separate topological database for each area to which it is connected.
In Figure 10, the ABRs belong to different non-backbone areas. R2 is in area 0.0.0.1, a not-so-stubby area (NSSA): R3 is in area 0.0.0.3: and R4 is in area 0.0.0.2, a stub area.
The NSSA (0.0.0.1) consists of two routers: R1 and R2. An NSSA allows external routes to be flooded within its area. These routes are then leaked to other areas within the AS. However, external routes learned from other areas within the AS do not enter the NSSA.
The stub area (0.0.0.2) consists of two routers: R4 and R5. A stub area does not allow external routes to be flooded within its area. A stub area is useful when much of the AS consists of external LSAs because it reduces the size of the topological database within the stub area and subsequently the amount of memory required by the routers in the area.
Area 0.0.0.3 is a non-backbone area consisting of two routers: R3 and R6.
External Routers A and B reside outside the AS. When an OSPF router exchanges routing information with routers in other ASs, that router is called an autonomous system boundary router (ASBR). The ASBRs shown in Figure 10 are R1 and R6.
Figure 11 provides interface and IP address information for the example OSPF network topology used for the procedures in this section.
Steps To Take
To verify that OSPF is configured correctly on routers in different areas of the network, follow these steps: