Enhanced Interior Gateway Routing Protocol (EIGRP)

• Classified as Advances Distance Vector
  • How far (how many hops) in a specified direction
• Considers bandwidth & delay
• Uses Diffused Update Algorithm (DUAL)
• Load, MTU & reliability are optional factors
• Very fast convergence
  • If we lose our primary path we have a backup to use instantly
• Used to be proprietary
• Cisco proprietary

EIGRP Tables

• Neighbor Table
  • IP addresses of directly attached neighbors
• Topology Table
  • EIGRPs database of routing information
  • Routes may be active or passive
    • Active means there is something that is still calculating something
    • A passive route is a route you can trust.
  • Only the best routes make it into the routing table

EIGRP Advantages

• Automatic neighbor discovery
• Sophisticated metric
  • "k values"
• Flexible summarization
  • In OSPF, only ABR routers can perform summarization.
  • In EIGRP you can use summarization everywhere
• Up to 16 feasible successors (4 by default)
• Open standard
• Supports load-sharing (unequal-cost load balancing)
  • Load balancing suggests there is an intelligent algorithm running and directing traffic intelligently
  • Load sharing is basically just instead of using one path, we use multiple paths
    • For example if its odd go left, if its even go right.
    • There is no guarantee of where traffic is going with load sharing.

Cisco EIGRP Configuration

router eigrp 10
	network 10.1.1.0 0.0.0.255
	no auto-summary

• By default, EIGRP does automatic summarization
• It is a best practice to disable automatic summarization to prevent possible loops