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EIGRP Routing

EIGRP automatically exchanges routes between routers - uses bandwidth and delay to calculate the best path (faster convergence than OSPF for large networks).

Why Use EIGRP?

Section titled “Why Use EIGRP?”

You need EIGRP when:

  • You have a Cisco-only network
  • You want faster convergence than OSPF
  • You need unequal-cost load balancing (variance feature)
  • Your network is very large and you want efficient routing updates

When to use EIGRP vs OSPF: EIGRP is faster and uses less CPU/bandwidth, but only works on Cisco routers. OSPF is an open standard that works with any vendor.

Enable EIGRP

Section titled “Enable EIGRP”
Router(config)# router eigrp 100
Router(config-router)# no auto-summary
Router(config-router)# eigrp router-id 1.1.1.1

Parameters:

  • 100 - AS (Autonomous System) number. Can be 1-65535. All EIGRP routers in the same domain MUST use the same AS number.
  • 1.1.1.1 - Router ID. Replace with a unique ID for each router.

Autonomous System (AS) number (100): Must match on all routers in the EIGRP domain.

auto-summary: Disabled by default in modern IOS. Always explicitly disable it with no auto-summary to prevent classful summarization issues.

Add Networks to EIGRP

Section titled “Add Networks to EIGRP”
Router(config-router)# network 10.1.1.0 0.0.0.255
Router(config-router)# network 192.168.10.0 0.0.0.255

Format: network [network address] [wildcard mask]

Add all interfaces (wildcard 0.0.0.0 means exact match):

Router(config-router)# network 10.1.1.5 0.0.0.0

Passive Interfaces

Section titled “Passive Interfaces”

Stop EIGRP from sending hello packets on interfaces where no EIGRP neighbors exist.

Make specific interface passive:

Router(config-router)# passive-interface GigabitEthernet0/0/0

Make all interfaces passive, then enable only needed ones:

Router(config-router)# passive-interface default
Router(config-router)# no passive-interface GigabitEthernet0/0/1
Router(config-router)# no passive-interface Serial0/1/0

Hello and Hold Timers

Section titled “Hello and Hold Timers”

EIGRP uses hello packets to detect neighbors.

Default timers:

  • Hello: 5 seconds (high-speed links), 60 seconds (low-speed links)
  • Hold: 15 seconds (high-speed), 180 seconds (low-speed)

Change timers on interface:

Router(config-if)# ip hello-interval eigrp 100 3
Router(config-if)# ip hold-time eigrp 100 10

⚠️ Timers don’t need to match on both sides (unlike OSPF), but it’s best practice to keep them consistent.

Bandwidth Configuration

Section titled “Bandwidth Configuration”

EIGRP metric calculation uses bandwidth. Set correct bandwidth on serial interfaces.

Router(config-if)# bandwidth 1544

Value in Kbps. Example: T1 = 1544 Kbps, E1 = 2048 Kbps.

Manual Summarization

Section titled “Manual Summarization”

Reduce routing table size by summarizing multiple networks.

On the interface sending the summary:

Router(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0

This summarizes 192.168.0.0/24 through 192.168.3.0/24 into one route.

Default Route Propagation

Section titled “Default Route Propagation”

Advertise a default route into EIGRP.

First, create a default static route:

Router(config)# ip route 0.0.0.0 0.0.0.0 203.0.113.1

Then redistribute it into EIGRP:

Router(config-router)# redistribute static

Load Balancing

Section titled “Load Balancing”

EIGRP supports equal-cost and unequal-cost load balancing.

Equal-cost load balancing (default, up to 4 paths):

Router(config-router)# maximum-paths 4

Unequal-cost load balancing (variance):

Router(config-router)# variance 2

Variance of 2 means EIGRP will load-balance across paths with metrics up to 2x the best path’s metric.

Authentication

Section titled “Authentication”

Secure EIGRP with MD5 authentication.

Create key chain:

Router(config)# key chain EIGRP-KEY
Router(config-keychain)# key 1
Router(config-keychain-key)# key-string SecurePass123
Router(config-keychain-key)# exit
Router(config-keychain)# exit

Apply to interface:

Router(config)# interface GigabitEthernet0/0/1
Router(config-if)# ip authentication mode eigrp 100 md5
Router(config-if)# ip authentication key-chain eigrp 100 EIGRP-KEY

Verify Configuration

Section titled “Verify Configuration”
Router# show ip eigrp neighbors
Router# show ip eigrp topology
Router# show ip eigrp interfaces
Router# show ip route eigrp
Router# show ip protocols
Router# show ip eigrp traffic

Troubleshooting

Section titled “Troubleshooting”

Neighbors not forming? Check:

  • AS numbers match
  • Authentication (if configured) matches
  • K-values match (default: K1 and K3 enabled)

Verify neighbor states:

Router# show ip eigrp neighbors

Clear EIGRP neighbors (force re-election):

Router# clear ip eigrp neighbors

Example Full Configuration

Section titled “Example Full Configuration”
Router(config)# router eigrp 100
Router(config-router)# eigrp router-id 1.1.1.1
Router(config-router)# no auto-summary
Router(config-router)# network 10.1.1.0 0.0.0.255
Router(config-router)# network 192.168.10.0 0.0.0.255
Router(config-router)# passive-interface default
Router(config-router)# no passive-interface GigabitEthernet0/0/1
Router(config-router)# maximum-paths 4
Router(config-router)# variance 2
Router(config-router)# exit


Router(config)# interface Serial0/1/0
Router(config-if)# bandwidth 1544
Router(config-if)# ip hello-interval eigrp 100 5
Router(config-if)# ip hold-time eigrp 100 15