EIGRP Summary - Shooting Yourself in the Foot

During my lab session the other night I was bitten by EIGRP summary routes and it took a little bit for me to wrap my head around what happened. So I figured it was a good idea to blog about the unexpected behavior.

The topology is as follows:

  • R1, R2 and R3 run EIGRP AS 100 on all interfaces. Auto-summary is disabled
  • R1 is the Internet facing router and generates a default route via EIGRP 
  • R1 connects two internal networks, and
  • R2 connects two internal networks, and