7.1 EIGRP Features and Operation

• EIGRP includes the subnet mask in its route updates
• EIGRP is hybrid routing protocol (has characteristics of both distance-vector & link-state protocols)
• EIGRP sends distance-vector updates containing info about networks plus cost of reaching them from the perspective of advertising router and synchronizes routing tables between neighbors at startup and then send specific updates only when topology changes occur
• EIGRP has a max hop count of 255 ( default = 100)
• EIGRP main features:

• EIGRP supports different network layer protocols (IP, IPX, AppleTalk & IPv6) through the use of PDM (protocol-dependent module)
• Each EIGRP PDM will maintain a separate series of tables containing the routing info that applied to a specific protocol
• EIGRP neighbor-ship establishment conditions: (Hello or ACK received; AS numbers match; Identical metrics (K values))
• Feasible distance: Best metric along all paths to a remote network, including the metric to the neighbour that is advertising that remote network
• Reported/advertised distance: Metric of a remote network, as reported by a neighbor
• Neighbor table: Each router keeps state info about adjacent neighbors
• Topology table: populated by PDM and acted upon by Diffusing Update Algorithm (DUAL)
• Feasible successor: path whose reported distance is less than the feasible route, and it's considered a backup route
• Succesor: best route to a remote network
• EIGRP uses a proprietary protocol called Reliable Transport Protocol (RTP) to manage the communication of message between EIGRP-speaking routers
• EIGRP uses Diffusing Update Algorithm (DUAL) for selecting and maintaining the best path to each remote network
• DUAL features: