EIGRP

Concepts and Planning

Why You Would Choose to Use EIGRP

  1. Backup routes (Fast convergence / DUAL)

  2. Simple configuration

  3. Flexibility in summarization

  4. Unequal cost load-balancing

  5. combines best of distance vector and link state

EIGRP Tables and Terminology

A router running EIGRP maintains three tables:

  • Neighbour table

  • Topology table (Successor routes, Feasible successor)

  • Routing table

A router running EIGRP has different terms:

  • Feasible Distance (FD)

    • Distance from you to reach a specific route

  • Advertised Distance (AD)

    • Distance from your neighbour to reach a specific route

  • Successor

  • Feasible Successor

  • Active Route (Bad - actively looking for a backup)

  • Passive Route (Good)

Note

To be considered a feasible successor, the AD must be less than the FD of the successor.

EIGRP Neighbour Relationships

  • Hello: forms relationship

  • Update: sends updates

  • Query: asks about routes

  • Reply: response to a query

  • Ack: acknowledges the update, query and reply messages

  • 224.0.0.10

EIGRP Metric Calculation

  • Bandwidth (K1)

  • Delay (K3)

  • Reliability (K4 and K5)

  • Loading (K2)

  • MTU

\[Metric = [(K1*BW+\frac{K2*BW}{256-load}+K3*delay)*\frac{K5}{K4+reliability}]\]
\[Real (default) Metric = [256*(slowestBW+AllLinkDelays)]\]
\[BW = \frac{10^7}{BW}\]
\[Delay = DelayInMicroseconds\]

Basic Configuration

_docs/eigrp-basic-configuration.zip

EIGRP Basic Configuration

BB Router

BB#conf t
BB(config)#int s1/0
BB(config-if)#ip add 10.1.24.1 255.255.255.252
BB(config-if)#band 256
BB(config-if)#no shut
BB(config-if)#int s1/1
BB(config-if)#ip add 10.1.34.1 255.255.255.252
BB(config-if)#band 128
BB(config-if)#no shut
BB(config-if)#int lo1
BB(config-if)#ip add 172.30.0.1 255.255.255.0
BB(config-if)#int lo2
BB(config-if)#ip add 172.30.1.1 255.255.255.0
BB(config-if)#int lo3
BB(config-if)#ip add 172.30.2.1 255.255.255.0
BB(config)#router eigrp 90
BB(config-router)#passive-interface default
BB(config-router)#no passive-interface s1/0
BB(config-router)#no passive-interface s1/1
BB(config-router)#variance 2
BB(config-router)#network 10.1.2.1 0.0.0.0
BB(config-router)#network 10.1.24.1 0.0.0.0
BB(config-router)#network 10.1.34.1 0.0.0.0
BB(config-router)#network 172.30.0.0 0.0.3.255
BB(config-router)#network 192.168.1.0 0.0.0.255
BB(config-router)#no auto-summary
BB(config)#ip route 192.168.1.0 255.255.255.0 null0
BB(config)#ip default-network 192.168.1.0
BB#wr

R2 Router

R2#conf t
R2(config)#int s1/0
R2(config-if)#ip add 10.1.24.2 255.255.255.252
R2(config-if)#band 256
R2(config-if)#no shut
R2(config-if)#int f0/0
R2(config-if)#ip add 10.1.2.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#int f0/1
R2(config-if)#ip add 10.1.25.2 255.255.255.0
R2(config-if)#no shut
R2(config-if)#router eigrp 90
R2(config-router)#passive-interface f0/1
R2(config-router)#network 10.1.2.2 0.0.0.0
R2(config-router)#network 10.1.24.2 0.0.0.0
R2(config-router)#no auto-summary
R2#wr

R3 Router

R3#conf t
R3(config)#int s1/0
R3(config-if)#ip add 10.1.34.2 255.255.255.252
R3(config-if)#band 128
R3(config-if)#no shut
R3(config-if)#int f0/0
R3(config-if)#ip add 10.1.2.3 255.255.255.0
R3(config-if)#no shut
R3(config-if)#router eigrp 90
R3(config-router)#network 10.1.2.3 0.0.0.0
R3(config-router)#network 10.1.34.2 0.0.0.0
R3(config-router)#no auto
R3#wr

Advanced Configuration

Frame Relay PVC Design

EIGRP Frame Relay PVC Design

  • Hub-and-Spoke

    • Inexpensive

    • If hub fails, WAN fails

  • Full Mesh

    • Expensive

    • Full redundancy

    • Good for VOIP

    • Seen in MPLS

  • Partial Mesh

    • Hybrid

    • Not so critical spokes have no redundancy

How EIGRP Handles NBMA (Non Broadcast Multi-Access)

  • EIGRP uses “Pseudo-Broadcasts” or manual neighbours (emulated broadcast)

  • Split Horizon can be an issue (“I will not tell somebody what they told me”)

    • Disabled on physical interfaces

    • Enabled on sub-interfaces

Best Practices and Design

Debugging EIGRP packets

Show communication of EIGRP packets:

debug eigrp packets

Query Swarm Resolutions

  1. Summary routes

  2. Stub configuration

Configuring Stubs

R1(config)#router eigrp1
R1(config-router)#eigrp stub
     connected and summary by default, which is recommended (used 99% of time)
     eigrp stub receive-only is the ultimate stub (similar to passive-interface)