EIGRP is a proprietary distance vector routing protocol developed by Cisco that uses DUAL algorithm. It provides fast convergence using neighbor adjacencies, variable length subnet masking, and supports authentication using MD5. The metric formula takes bandwidth, delay, reliability, load, and MTU into consideration to determine the best path. EIGRP configuration allows tuning of K values, summarization, stub routing, authentication, and interface settings. Troubleshooting commands include show ip eigrp to display neighbor, topology, and traffic information.

1. EIGRP packetlife.net
Protocol Header Attributes
8 16 24 32 Type Distance Vector
Version Opcode Checksum
Algorithm DUAL
Flags
Internal AD 90
Sequence Number
External AD 170
Acknowledgment Number
Summary AD 5
Autonomous System Number
Standard Cisco proprietary
Type Length
Protocols IP, IPX, Appletalk
Value
Transport IP/88
Metric Formula Authentication MD5
K2 * bw K5 Multicast IP 224.0.0.10
256 * (K1 * bw + + K3 * delay) *
256 - load rel + K4 Hello Timers 5/60
· bw = 107 / minimum path bandwidth in kbps Hold Timers 15/180
· delay = interface delay in µsecs / 10
K Defaults Packet Types
EIGRP Configuration
K1 1 1 Update
Protocol Configuration
K2 0 3 Query
! Enable EIGRP
router eigrp <ASN> K3 1 4 Reply
! Add networks to advertise K4 0 5 Hello
network <IP address> <wildcard mask>
K5 0 8 Acknowledge
! Configure K values to manipulate metric formula
metric weights 0 <k1> <k2> <k3> <k4> <k5>
Terminology
Reported Distance
! Disable automatic route summarization The metric for a route advertised by a neighbor
no auto-summary
Feasible Distance
! Designate passive interfaces The distance advertised by a neighbor plus the cost
passive-interface (<interface> | default) to get to that neighbor
Stuck In Active (SIA)
! Enable stub routing
The condition when a route becomes unreachable
eigrp stub [receive-only | connected | static | summary]
and not all queries for it are answered; adjacencies
! Statically identify neighoring routers with unresponsive neighbors are reset
neighbor <IP address> <interface> Passive Interface
An interface which does not participate in EIGRP but
Interface Configuration whose network is advertised
! Set maximum bandwidth EIGRP can consume
ip bandwidth-percent eigrp <AS> <percentage>
Stub Router
A router which advertises only a subset of routes,
! Configure manual summarization of outbound routes and is omitted from the route query process
ip summary-address eigrp <AS> <IP address> <mask> [<AD>]
Troubleshooting
! Enable MD5 authentication show ip eigrp interfaces
ip authentication mode eigrp <AS> md5
ip authentication key-chain eigrp <AS> <key-chain> show ip eigrp neighbors
! Configure hello and hold timers show ip eigrp topology
ip hello-interval eigrp <AS> <seconds> show ip eigrp traffic
ip hold-time eigrp <AS> <seconds>
clear ip eigrp neighbors
! Disable split horizon for EIGRP
no ip split-horizon eigrp <AS> debug ip eigrp [packet | neighbors]
by Jeremy Stretch v2.1