CCNA 3.11: Configure, verify and troubleshoot EIGRP for IPv4


Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary advanced distance vector dynamic routing protocol.


Study Notes:

  • EIGRP uses the Diffusing Update Algorithm (DUAL)
    • Fast convergence
    • Easy on processor
    • Incremental updates
  • EIGRP is an Advanced Distance vector protocol
  • Combines the best of Distance Vector with Link State protocols, but is considered a Distance Vector protocol (Enhanced)
  • Simple to configure
  • Flexibility in summarization (not on CCNA, but good to know)
  • Unequal cost load balancing
  • Doesn’t age out routing entries
  • No periodic updates
  • 3 tables
    • Neighbor table - directly connected to the router
    • Topology table - all routes
    • Routing table - DUAL algorithm figures out best route
  • Uses backup path if one exists in topology table
  • Terminology
    • Feasible Distance (FD) - to reach the distant network
    • Advertise Distance (AD) - how far for neighbor to reach the network
    • Successor - primary path
    • Feasible Successor - backup path. To be considered a feasible successor, the AD must be less than the FD of the successor
    • Active Route - (bad) router is trying to find route to network
    • Passive Route - (good) router knows route to network
  • Important commands to know
    • show ip route - show the routing table
    • show ip route eigrp - show only EIGRP routing table entries
    • show ip eigrp neighbors - who are the directly connected neighbors
      • H = the order in which the neighbor was discovered
      • Hold = hold time in seconds waiting for a Hello packet
      • Uptime = length of time of neighbor relationship
      • SRTT = smooth round-trip timer
      • RTO = Retransmission Time Out, time between multicasts basd on SRTT
      • Q Cnt = how many messages are in the queue
      • Seq Num = sequence number of the last update
    • show ip eigrp interfaces - shows all interfaces that EIGRP is enabled on
    • show ip eigrp topology - shows all of the FD, AD, Successor, Feasible Successor, etc.
    • show ip eigrp traffic - shows number of EIGRP packets sent and received
    • show ip protocols - displays a summary of configured routing protocol information
  • EIGRP messages are sent via multicast
    • HELLO: forms the relationship
    • UPDATE: sends updates
    • QUERY: asks about routes
    • REPLY: response to a query
    • ACK: acknowledges UPDATE, QUERY and REPLY messages
  • EIGRP uses triggered updates instead of the entire table
  • EIGRP is its own layer 4 protocol (port 88). It doesn’t use TCP.
  • EIGRP metric - used K values
    • K1 - bandwidth (statically configured value). default = 1
    • K2 - delay (statically configured value; in 10s of microseconds). default =0
    • K3 - reliability (dynamic). default = 1
    • K4 - loading (dynamic). default = 0
    • K5 - MTU (packet size). default = 0
    • EIGRP Metric Calculation (not on CCNA):

256 * [(k1 * bw) + [(k2 * bw) / (256-load)] + k3 * delay)] * [k5 / (reliability + k4)]

  • For EIGRP neighbors to form, their k values must be equal
  • The CCNA does not cover EIGRP authentication, filtering, manual summarization, redistribution, stub)
  • Configuration:
R1#config t
    router eigrp 1 (AS number)
        network (classful)
        no auto-summary (keeps it from summarizing)


R2#config t
    router eigrp 1
        network (wildcard mask)

show ip protocols 
show ip route
show ip eigrp topology
show ip eigrp neighbors
show ip eigrp traffic



PacketTracer Lab: CCNA-3.11-Configure-verify-and-troubleshoot-EIGRP-for-IPv4.pkt

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