This section examines current best practices for IGP migration, referring to the exchange of a network’s existing, or legacy, IGP with a different version of IGP. Generally, the overall goals are to minimize network disruption while also taking the opportunity to improve on the network’s design and operation. The IGP plays a critical role in the operation of any IP network. Upgrading a legacy network’s IGP can result in dramatic performance improvements and new service capabilities, and can align a company with an open standards-based solution, which in turn facilitates a best-of-breed decision among networking boxes.
IGP migration is an excellent time to clean house, so to speak, by reevaluating all aspects of the current network’s design. Some factors to consider include:
The potential for readdressing to better accommodate hierarchical design and route summarization
The number and types of routers needed
How those routers interconnect (WAN/LAN technologies may have evolved since the original network deployment)
Ways to improve reliability
The need to maintain high network availability may preclude significant redesign. Usually a compromise must be reached between the need for availability versus potential optimizations, based on the specifics unique to each enterprise. In some cases, a new backbone is deployed in parallel (the integration model), which affords the luxury of complete redesign at the cost of additional gear.