EIGRP Overview

EIGRP overview

• DUAL aka Diffused update alogorythm
• Low CPU utilization
• Scalability
• Ease of configuration
• Composite metric
• Automatic summarization by default-by default eigrp acts in a classful manor and summarizes prefixes. Best practice is to turn this off using the (no auto summary command)

EIGRP Metric

• Five components
• Bandwidth
• Delay
• Reliability
• Load
• MTU

Eventually cisco changed it to bandwidth and delay. MTU is only there as a potential tie breaker. So realistically Bandwidth and delay make the metrics up. Bandwidth that is the weakest link bandwidth in the link. The lowest cost bandwidth is considered the bandwidth for that path. Administrators set the bandwidth.

Delay is the sum of delays for the entire path. We use the "delay" command to edit the delay value.

Composite metric edited with K values. You can edit each k value which is represented in the power of 3. To view default k values "show ip protocol". K values must match between eigrp speakers.

Note MTU does not have a corresponding K value.

EIGRP DUAL

• Feasible Distance (FD)= the cost between the local router and the destination prefix. Consist of the cost to the next hop, added to the cost that next hop is advertising to the local router (Advertised Distance or AD)
  

• Successor is the best (lowest cost) route to destination.

• Feasible Successor is the second best route.

Next hop must have AD less than the current FD of the successor. This is a loop prevention mechanism.

EIGRP "Show ip eigrp topology"

• Passive:network available
• Active:network unavailable
• Update:network is being updated
• Query:outstanding query-waiting for ACK
• Reply:generating a reply to a cry
• SIA:convergence problem aka (stuck in active)