n the design of the OSPF routing protocol, the number of routers in an area is widely discussed in deployments and forum, and according to recent studies and the power of modern routers, it is no longer a major concern. However, the number of routers in the backbone area 0 is still relevant. The backbone area in the OSPF world is critical and serves as the central point in a multi-area architecture, with direct connections to non-backbone areas (which is the core function of how the OSPF protocol operates) for the exchange of link-state information between non-zero areas, filtering, etc. This can lead to instability in the topology, an impact on convergence time, and potentially increased CPU utilization, as all inter-area information always passes through the backbone area.
Therefore, it is extremely prudent to consider this point and be cautious when adding routers to the backbone area. Best practices suggest reducing the number of routers and including only those that are necessary in addition to the ABRs.
Another critical point in the backbone area is the importance of redundancy to prevent partitioning of the backbone area in the event of a link failure. A good design for a backbone area ensures that no single link failure can cause a partition in area 0, which implies that a full mesh between the routers would be ideal. In the example below, if the link between R4 and R5 fails, the exchange of link-state information and communication among the internal routers of area 0 would be disrupted due to the inter-area loop prevention rule, which states that an ABR always ignores Type-3 LSA learned from another ABR through a non-backbone area.
2 Comments
