Overview of EIGRP

Enhanced Interior Gateway Routing Protocol - (EIGRP) 

 Cisco proprietary routing protocol
Advance distance vector
32 bit metric
DUAL algorithm for path calculation
Bandwidth,delay,reliability,load,MTU are metric
using WILD CARD MASK insted of subnet mask in configuration
Classless inter-damain routing
 support three tables
Neighbor,Topology and Routing table


EIGRP has four basic components:

• Neighbor Discovery/Recovery
  
• Reliable Transport Protocol
  
• DUAL Finite State Machine
  
• Protocol Dependent Modules
  
  
  EIGRP uses five packet types:
  
  • Hello/Acks
    
  • Updates
    
  • Queries
    
  • Replies
    
  • Requests
      

  • Router# conf t
    Router(config)# router eigrp {AS number}
    Router(config-router)# network 192.168.0.0 0.0.255.255

    Metric = [BandW +Delay]  ×  256

    The EIGRP transport mechanism uses a mix of multicast and unicast 
    packets, using reliable delivery when necessary. All transmissions use 
    IP with the protocol type field set to 88. The IP multicast address used
     is 224.0.0.10. 

    The default behavior of EIGRP is to summarize on network-number boundaries

    A route is regarded as stuck-in-active (SIA) when DUAL does not receive a
     response to a query from a neighbor for three minutes, which is the 
    default value of the active timer. DUAL then deletes all routes from 
    that neighbor, acting as if the neighbor had responded with an 
    unreachable message for all routes. 

    EIGRP limits itself to using no more than 50% of the configured bandwidth on router interfaces

    EIGRP offers the following radical improvements over RIP and IGRP:
  • Fast convergence--convergence is almost instantaneous when a feasible successor is available.
  • Variable Length Subnet Masks are supported--subnet mask information is exchanged in EIGRP updates. This allows for efficient use of the address space, as well as support for discontiguous networks.
  • Route summarization at arbitrary bit boundaries, reducing routing-table size.
  • No regular routing updates--network bandwidth and router CPU resources are not tied up in periodic routing updates, leading to improved network manageability.
  • Ease of configuration--EIGRP can be configured with almost the same ease as IGRP. However, troubleshooting DUAL can be difficult.
  
  
  These EIGRP benefits come at the price of higher memory requirements (in addition to the routing table, EIGRP requires memory for the topology table and the neighbor table). DUAL is complex and can be very CPU-intensive, especially during periods of network instability when CPU resources are already scarce. Also, don't forget that the EIGRP is a Cisco proprietary protocol.
  EIGRP is in use today in several mid-sized networks.
  
  

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