Incremental SPF

In Chapter 1 we discussed partial shortest path first runs, which involve simply checking leaf nodes if a piece of external reachability changes, such as the connection to an IP network. It is also possible to run shortest path first calculations over just a portion of the best path tree in some circumstances; this operation is called an incremental SPF. Let's use the network illustrated in Figure 6-20 to consider the implications of running SPF over a small part of the best path tree, rather than the entire tree.

Figure 6-20. A network and its shortest path tree for incremental SPF consideration

Let's consider what would happen ...

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