Case Study: Migration of Areas
Although Integrated IS-IS requires each router to be in only one area, multiple NSAPs addresses (each with a different area ID) can be used simultaneously for the purpose of renumbering, splitting, or merging of areas. Using multiple NSAPs on an IS-IS router is also known as multihoming. In the default mode of operation, Cisco IOS allows up to three NSAP addresses, each with a different area ID but the same system ID. It should be stressed that configuring a router with more than one area address must be for only transitional situations. Multihoming is covered in detail in Chapter 4, “Addressing in Integrated IS-IS,” in the “Configuring Multiple Nets for a Single IS-IS Process” section.
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