EIGRP Routes/Load Balancing

• Feasibility Condition:
  • Used for selecting backup paths.
  • Pre-computed during DUAL
    • Advantages
      • Sub-second re-convergence when successor fails.
      • Fault isolation.
        • No need to speak with neighbors about additional paths.
      • Unequal cost distribution.
  • What the process is doing:
    • Find best path, hold onto local metric.
    • Find second best path.
      • Any router with metric lower than mine, they’re closer to destination.
      • Any router with metric equal or higher than mine, forget about them.

• Successor – Best Path
• Feasible Distance – Metric of Successor
• Reported Distance – Metric of neighbors
• Feasible Successor – Backup paths that meet Feasibility Condition

• Only Feasible Successors can be used for unequal cost load balancing

Reconvergence:

• If no FS:
  • Sends route into Active state
  • Sends QUERY to all neighbors
  • Reconverges from neighbor REPLY
• With FS:
  • No route Active
  • FS promoted to Successor
  • QUERY not generated
  • Results in sub-second convergence

Bandwidth and Delay

• Bandwidth
  • DUAL uses the lowest bandwidth along a path to a destination.
  • By prefix.
• Delay
  • DUAL uses delay by adding up hop by hop to destination.
  • Can be modified under interface with ‘delay’ command.

Unequal Load Balancing:

• Only Feasible Successors allowed.
• Controlled with Variance command.
  • FD * variance > FS, load balancing happens.

• Commands:
  • router eigrp <name>
    • address-family ipv4 autonomous-system <AS #>
    • topology base
    • variance <variance multiplier>