Just when you are considering some well-deserved time off, given the success of the recently deployed RIPv2 internetwork, you receive notification from the new CIO that the Beer-Co network must migrate to OSPF as part of a modernization initiative. Beer-Co has conducted a design review and determined that a single OSPF area with the ability to expand to a hierarchical design in the near future is required.
Considering the migration methods described in the previous section and the current design criteria, you propose an overlay-based migration. The reasons for this recommendation include the following:
Both the legacy and planned networks are flat.
Both the legacy Cisco and new Juniper Networks gear support the legacy and new IGPs.
It’s the most direct migration strategy, and you are still smarting from tilting at RIP.
Figure 6-9 shows the before, during, and after networks. In the middle, both IGPs are running, but altered preferences ensure that RIP routes remain active, which provides you the chance to verify all aspects of OSPF before its routes become active. The key to the overlay model is altered protocol preferences, and the figure also shows the beginning, initial modification, and final preference values for RIP and OSPF internal/external routes.
The critical point occurs before OSPF is activated (especially in IOS, where changes take effect immediately as they are entered). Both the internal and external preferences are set so that RIP ...