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EIGRP Stand for Enhanced Interior Gateway Routing Protocol

Type                          :Advanced Distance Vector Routing Protocol
AD Value                     :90
Hello Timer                  :60 sec
Update Timer               :None
Dead Timer                  :3 Hellos
Transport                    :88 (IP)
Multicast Add               :

EIGRP stands for Enhanced Interior Gateway Routing Protocol, it is also called balanced hybrid routing protocol or advanced distance vector routing protocol. It support for variable length subnet mask (VLSM), It maintain three type of tables i.e., neighbour table, topology table & routing table

  1. Neighbour – directly connected neighbour (feasible successor)
  2. Topology – all path reach to destination (feasible successor)
  3. Routing – best path (successor)

DUAL:  Diffusion update algorithm

  1. Successor is available in routing table
  2. If successor failed means it will take the feasible successor

DUAL Parameter

  1. A.D = Advertised distance (Reported Distance)
  2. F.D = Feasible distance

Reported Distance: The metric for a route advertised by a neighbour.
Feasible distance: The distance advertised by a neighbour plus the cost to get to that neighbour.

EIGRP Packet Types:

EIGRP uses five types of packet :

  • Hello—EIGRP uses hello packets in the discovery of neighbours. They are multicast to By default, EIGRP sends hello packets every 5 seconds (60 seconds on WAN links with 1544 Mbps speeds or less).
  • Acknowledgment—an acknowledgment packet acknowledges the reception of an update packet. It is a hello packet with no data. EIGRP sends acknowledgment packets to the unicast address of the sender of the update packet.
  • Update—Update packets contain routing information for destinations. EIGRP unicasts update packets to newly discovered neighbours; otherwise, it multicasts update packets to when a link or metric changes. Update packets are acknowledged to ensure reliable transmission.
  • Query—EIGRP sends query packets to find feasible successors to a destination. Query packets are always multicast.
  • Reply—EIGRP sends reply packets to respond to query packets. Reply packets provide a feasible successor to the sender of the query. Reply packets are unicast to the sender of the query packet.

EIGRP Summary

The characteristics of EIGRP follow:

  • Uses IP protocol 88.
  • Classless protocol (supports VLSMs).
  • Administrative distance is 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.
  • Hybrid routing protocol (distance vector that has link-state protocol characteristics).
  • Support for authentication.
  • Uses DUAL for loop prevention.
  • Default composite metric uses bandwidth and delay.
  • You can factor load and reliability into the metric.
  • Sends partial route updates only when there are changes.
  • By default, equal-cost load balancing. Unequal-cost load balancing with the variance command.
  • Potential routing protocol for the core of a network; used in large networks.

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