EIGRP: Local Computation

If a new neighbor comes online advertising a lower cost path to a destination, and passes the FC the path through the new neighbor is deemed as a Feasible Successor.  The router then performs the following steps:

  1. The Feasible Successor providing the least CD is made the new Successor
  2. If the CD over the new Successor is less than the current FD, the FD is updated with the new CD, otherwise the FD does not change.
  3. The routing table is updated to point toward the new Successor route
  4. If the current distance to  the destination has changed as a result of switching to a new Successor, Update messages are then sent to all neighbors advertising the updated distance to the destination.

These actions are performed solely using information already stored in the router’s topology table without having to coordinate with other routers.

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