Network Sales and Services Handbook (Cisco Press Networking Technology)

EIGRP stores routing-related information in three tables, each dedicated to the organization and storage of network data. These tables are as follows:

• Neighbor Table Neighbor relationships are tracked in this table and provide the basis for all of EIGRP's routing update and convergence activities.

• Routing Table This contains least-cost routes that DUAL calculated for all known destinations. EIGRP tracks up to six routes to each destination.

• Topology Table This stores all information needed to calculate a set of distances and vectors to all known and reachable destinations. This information includes the following:

  - Bandwidth The bandwidth of the slowest interface in the path to a destination.

  - Total Delay The total of delay expected in that route.

  - Reliability Path reliability identical to the IGRP Reliability metric.

  - Load Load of the path.

  - MTU (Maximum Transmission Unit) The size of the smallest MTU supported by the router interfaces in the path. EIGRP will notify all routers in advance of the maximum MTU on each path to a given destination.

  - Reported Distance The distance reported by an adjacent neighbor to a specific destination. This metric does not include the distance between this originating (advertising) router and the adjacent neighbor.

  - Feasible Distance The lowest calculated metric to each destination.

  - Route Source The identification number of the router that originally advertised a route. This field is populated only for routes learned from outside the EIGRP network.

Topology table entries are in one of two states:

• Active A route currently being recomputed; the process of recalculating routes in search of new successors. This process is time- and resource-intensive. DUAL is designed to use any and all available feasible successors before recomputing routes. Recomputing will occur only when there are no successors, feasible or otherwise, to a route.

• Passive A route currently stable and available for use.