• Hello/Ack
    • Neighbor Discovery
    • Multicast advertised on segment, and Unicast responses are returned.
    • Hello with no Data is Ack.
    • Also Keepalive.
  • Updates
    • Conveys reachability information for each destination.
    • Sent reliably.
  • Queries
    • Sent out to search for another path during convergence.
    • Multicast looking for missing prefix.
  • Replies
    • Sent in response to Query, brings prefix from active back to passive (good).
    • Sent reliably.
  • Request
    • Used to obtain specific information from neighbor.

Stuck in Active:

  • EIGRP router goes into SIA state and removes neighbor adjacency if it does not receive response to query after 3 minutes.
  • Continues propagation of query traffic across EIGRP domain.
  • Condition where EIGRP router goes active for specific route by sending query, but never receives a reply.

EIGRP Graceful Shutdown

  • Enabled by Default
  • Neighbor will receive ‘PEER-TERMINATION’ message, implies EIGRP was turned off on interface, do not wait for hold timers.
  • Does not work with an interface shutdown. Has to be removal of EIGRP interface or process.


  • Multiple paths in RIB for same destination prefix – ECMP


  • Installation of both successor routes and feasible successors into the EIGRP RIB.
  • Variance value can be modified to enable this feature. Variance value is the FD (best available route metric – successor) multiplied by the variance multiplier.
    • Any feasible successor’s FD with metric below EIGRP variance value is installed into RIB.
    • Feasible Successor needs FD to be less than successor route multiplied by variance value.

EIGRP Stub Routing:

  • Stub router will advertise all connected and summary routes to upstream EIGRP speakers (Default).
  • Stub router never gets queried by upstream EIGRP speakers for route information.
  • Helps with using branch as traversal for link failure.
  • Branch(config-router)#eigrp stub (default advertise connected and summary)

EIGRP Finite State Machine:

  • All the states and processes that DUAL uses to compute metrics and routes.
  • Passive route states equate to a stable network and no re-computation being needed by DUAL.
  • Active route states equate to DUAL re-computing metrics and/or locations for routes.
    • No feasible successor begins query to EIGRP neighbors.

EIGRP Add Path:

  • DMVPN Feature
  • Allows for load balancing traffic between two spokes over EIGRP.
  • By default a hub will not advertise more than one route to a spoke destination, even if the hub has two equal cost paths. If a spoke lost a primary route EIGRP would have to reconverge.
  • Configure:
    • HubRouter(config)#router eigrp NAMEMODE
    • HubRouter(config-router)#address-family ipv4 unicast autonomous-system 1
    • HubRouter(config-router-af)#af-interface tunnel1
    • HubRouter(config-router–af-interface)#add-paths <number of paths>


  • Allows for taking a backup path in the network within 50ms
  • Installs both the Successor and Feasible Successor in the routing table, not just successor. Lowers failover time.
  • Interior Gateway Protocols calculate LFAs using 2 methods:
    • Per-Link:
      • Found in multiaccess segments.
      • All links use the same next hop address.
      • Single secondary backup link.
      • Less CPU and simple to calculate.
    • Per-Prefix
      • Calculates LFA for each destination.
      • Enforces FRR or failover uses two different backup routes or next hops.
  • If there are multiple LFAs then FRR needs to choose one. List of tie breakers below, lower metric wins:
    • Interface Disjoint
      • Do not choose an LFA that goes out the same interface – 20
    • Linecard Disjoint
      • Do not select LFA that exits out same line card – 40
    • Lowest Repair Path Metric
      • Choose LFA with lowest metric – 30
    • Shared risk Link Group (SRLG)
      • Prefer LFA not sharing the same Share Link Group

EIGRP Summary Leak Map

  • Advertises more specific route(s) on interface in addition to summary.
    • 1 – Create access list
      • R1(config)#ip access-list standard Leak
      • R1(config-std-nacl)#permit
    • 2 – Create Route Map referencing access list
      • R1(config)#route-map Leak-Example 10
      • R1(config)#match ip address Leak
    • 3 – Use summary command under interface
      • R1(config)#interface Gig0/2
      • R1(config-if)#ip summary-address eigrp 1 leak-map Leak-Example
  • In the routing table of neighbor there is now a summary address ( and a longer prefix route of


  • Typical EIGRP configuration for branch routers.
  • Way to stop queries from being sent to a router when there are topology changes or links going down.
  • Types of EIGRP Stub networks:
    • Redistribute – Stub router can advertise redistributed routes.
    • Summary – Stub router can advertise summary routes.
    • Connected – Stub router can advertise directly connected.
    • Static – Stub router can advertise redistributed static routes.
    • Receive-only – Stub router does not advertise any networks, only receives.
  • Default ‘eigrp stub’ command uses connected and summary.

EIGRP Stub Leak-Map

  • Similar to EIGRP Summary leak map, allows router to be configured as stub but still have exceptions for routes being advertised.
  • R1(config)#router eigrp 1
  • R1(config-router)#eigrp stub leak-map <name of created route-map>

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