CCNA Design Lab: EIGRP vs OSPF for Branch Networks

Choosing between EIGRP and OSPF for branch network design is a foundational decision that affects convergence behavior, bandwidth consumption, CPU load, and operational complexity. Both protocols are production-grade and appear on CCNA exams, but their strengths differ significantly depending on your network topology, vendor mix, and failover requirements. This lab-focused guide walks through the key decision points.

Protocol Fundamentals and Administrative Distance

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary distance-vector protocol with fast convergence and low overhead. OSPF (Open Shortest Path First) is an open-standard link-state protocol that scales to large networks and works across any vendor platform. Both use different metrics: EIGRP combines bandwidth, delay, reliability, and load; OSPF uses cost derived from link bandwidth. By default, EIGRP has an administrative distance of 90 for internal routes, while OSPF uses 110. This means EIGRP routes are preferred when both protocols run on the same router, a critical detail in multi-protocol migration labs.

Convergence and Failover Behavior

• →EIGRP: typical convergence under 1 second with feasible successors
• →OSPF: typical convergence 2-5 seconds depending on SPF throttling
• →EIGRP: lower bandwidth overhead (partial updates only)
• →OSPF: higher initial overhead (full LSA floods) but stable in steady state

Scalability and Design Constraints

Lab Design Decision Framework

! EIGRP Branch Configuration Example
router eigrp 100
  network 10.0.0.0 0.0.255.255
  passive-interface default
  no passive-interface GigabitEthernet0/0
  eigrp router-id 10.1.1.1

! OSPF Branch Configuration Example
router ospf 1
  router-id 10.1.1.1
  network 10.1.1.0 0.0.0.255 area 0
  network 10.2.1.0 0.0.0.255 area 1

In practice, many enterprises run both protocols: EIGRP in the core for speed, OSPF at the edge for multi-vendor compatibility. Your CCNA labs should test both scenarios. Understanding administrative distance is essential when protocols overlap; lower AD wins the routing table. Use the reference tool below to internalize how AD affects route selection during failover and redistribution events.