• Fast Convergence
• Partial triggered udpates
• Multiple protocol support (Ipv4/6, appletalk, IPX)
• Multicast and Unicast (communications between routers)
• VLSM support (classless)
• Datalink layer protocol and topologies – no extra config it just works (eg: FR, broadcast, non broadcast, LAN, WAN)

Four Key Technologies

• Neighbour discovery/re-discovery – hello packets
• RTP – reliable transport protocol
• Dual finite state machine – Decision process for ALL route communications
• PDMs – Protocol dependant modules, IPv4/6,appletalk, ipx all operate independantly of each other

EIGRP Operation

For IP routing the process is:

Routing Information -> EIGRP Neighbour Table -> Topology Table -> Routing Table

• Neighbour table, all adjacent neighbours
• Topology Table, all learned routes to all destinations
• Routing Table, best route to each destination

Successor = Best route (least cost path)
Feasible Successor = 2nd best route (backup route)
Feasible Distance = The metric of the successor route

The routing table is essentially a subset of the topology table

The topology table stores the RIB of each neighbour, the AD for each distination and the FD> to reah each destination.

Eigrp Packets

Hello – multicast discovery
Update – route changes, sent only to affected routers
Query – RTP, multicast then unicast, look for a successor route
Reply – Response to query, unicast, RTP
Ack – Acknowledge update/query/reply, unicast

All EIGRP overhead traffic is generated through the primary interface address

All packets carrying routing information are sent reliably

Retransmission of a reliable packet occurs up to 16 times or until the hold timer expires. After 16 tries the router resets the neighbourship.

DUAL Feasibility Condition

If your metric is lower than mine, you are loop free

Advertised Distance (AD) = Metric from the neighbour routers point of view
Local Distance = Metric to reach the neighbour

Dual Metric Calculation

Bandwidth (lowest link in Kbps) + Delay (in 10s of microseconds)

K Values

K1 & K3 = 1
K2 & K4 & K5 = 0
Identical K values are required to for an adjacency

Planning EIGRP Implemenations

• IP Addressing Plan
• Network TOpology
• EIGRP Traffic Engineering

Verifying EIGRP Operation

show ip route eigrp
show ip eigrp neighbors
show ip eigrp interfaces
show ip eigrp topology [all-links]
show ip eigrp traffic
show ip protocols

debug ip eigrp
debug eigrp packets
debug ip eigrp summary
debug ip eigrp neighbors

EIGRP Commands

ip default-network – candidate default route
ip summary-address – sumarise on an interface
ip bandwidth-percent eigrp [as] [%] – percentage of interface bandwidth used for eigrp operations (updates/queries/replies)
no ip split-horizon eigrp [as] – turn off split horizon for multi-point FR
ip authentication mode eigrp [as] md5 – enable md5 authentication on the interface
ip authentication key chain eigrp [as] [key chain name] – specify the key chain to use for eigrp authentication

General Notes

Key chain authentication is configured globally and then added per interface
The summary route will stay in the RIB as long as one of the summarised prefixes is still reachable
Summary route have a default AD = 5

All IP routing protocols on Cisco routers can perform equal cost load balancing.

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