OSPF vs EIGRP — which one for CCNA and real US networking work

The CCNA 200-301 blueprint expects you to know both OSPF and EIGRP. The interview question US recruiters ask (“if you had to pick one for a greenfield network, which and why?”) expects a real opinion. Here’s the honest read on when each wins and how to answer.

The short version

• OSPF — open standard (RFC 2328 / RFC 5340 for v3). Link-state. Runs everywhere. Slower to converge without tuning, more predictable at scale.
• EIGRP — Cisco proprietary (now RFC 7868 informational). Advanced distance-vector using DUAL. Blazing fast convergence with Feasible Successors. Only makes sense on Cisco-only networks.

If your enterprise is Cisco-only and stays that way: EIGRP is faster to converge and simpler to run. If you have any non-Cisco routers (Juniper, Arista, Palo Alto, cloud vendors): OSPF is the only option.

The CCNA exam scope for each

OSPF (200-301) — expect deep questions:

• Single-area configuration (router ospf 1, network <ip> <wildcard> area <n>)
• Router-ID selection (manual → loopback → highest active interface IP)
• Neighbor states (DOWN → INIT → 2WAY → EXSTART → EXCHANGE → LOADING → FULL)
• DR / BDR election on broadcast networks
• Cost calculation (10^8 / bandwidth default)
• Hello / Dead timer defaults (10 / 40 on broadcast, 30 / 120 on non-broadcast)
• LSA types 1, 2, 3 (basic), 5 (external)
• Multi-area basics (backbone area 0, ABR, ASBR)

EIGRP (200-301) — narrower:

• Configuration (router eigrp 100, network, wildcard masks)
• K-values (default: K1=1, K3=1, others 0) — must match between neighbors
• Metric formula (bandwidth + delay in default)
• Successor + Feasible Successor + Feasibility Condition
• Neighbor formation (Hello / Hold, must match Kvalue + AS number)
• AD 90 internal, 170 external

Real weighting on the exam: OSPF is ~10-12 questions typically, EIGRP is ~4-6. Study OSPF deeper.

Where each actually lives in US enterprise networks

OSPF is used at:

• ISPs (backbone routing, OSPFv3 for IPv6)
• Multi-vendor enterprises — Fortune 500 with Cisco + Juniper + Arista mix
• Government / DoD contractors (open standard is a requirement in many RFPs)
• Any greenfield network built after ~2018 where cloud connectivity is a factor

EIGRP is used at:

• Legacy Cisco-only enterprises (banks, healthcare, universities with 20+ year Cisco relationships)
• Cisco SD-WAN underlays
• Cisco DMVPN networks (EIGRP over the tunnel)
• Retail chains with Cisco Meraki + traditional Cisco IOS mixed

In practice: any US networking role you interview for will use ONE of them for the interior gateway. Ask in the interview which — it’s a smart question, and the answer tells you a lot about how the network was designed.

Head-to-head technical comparison

Feature	OSPF	EIGRP
Protocol type	Link-state	Advanced distance-vector (DUAL)
Vendor	Open (IETF)	Cisco-proprietary (RFC 7868 informational)
AD (default)	110	90 internal / 170 external
Metric	Cost from bandwidth	Composite (BW + delay by default)
Convergence	5-40 s untuned; sub-second with BFD	Sub-second natively (FS installs instantly)
Multicast for updates	224.0.0.5, 224.0.0.6	224.0.0.10
Transport	Directly over IP (protocol 89)	Directly over IP (protocol 88)
Neighbor timers (default)	Hello 10 / Dead 40	Hello 5 / Hold 15
Loop prevention	SPF algorithm on link-state database	Feasibility Condition (RD < FD)
Load balancing	Equal-cost only (up to 16 paths)	Equal AND unequal cost (variance keyword)
Auto-summary	No (never had it)	Historically yes, disabled by default since IOS 15
Router-ID	Explicit — needed for adjacency + LSDB	Automatically chosen but shown in show ip eigrp
Hierarchy	Area-based (backbone area 0)	Flat by default; can use stubs
IPv6	OSPFv3 (uses link-local for neighbor comms)	EIGRP for IPv6 (address-family syntax)

When OSPF wins

• Multi-vendor network — the only sensible choice.
• Very large network needing hierarchy — areas + LSAs give you structural containment.
• Predictable, well-documented behavior — everyone in the industry knows OSPF.
• Cloud interconnect — AWS Direct Connect, Azure ExpressRoute, GCP Cloud VPN all support OSPF and BGP; none support EIGRP.

When EIGRP wins

• All-Cisco environment — simpler config, faster convergence out of the box.
• DMVPN / Cisco SD-WAN — Cisco optimized EIGRP for their overlay technologies.
• Uneven bandwidth links — unequal-cost load balancing via variance is genuinely useful (OSPF has no equivalent).
• Fast pre-computed backup paths — Feasible Successor logic. When your Successor dies, DUAL installs the FS in milliseconds without recomputation.

The interview question — how to answer

“You’re designing an interior routing protocol for a new enterprise network. OSPF or EIGRP — pick and defend.”

Wrong answer: “OSPF because it’s the standard.”

Better answer: “Depends on the environment. For a greenfield, multi-vendor, or cloud-connected enterprise, OSPF — because it’s open and integrates with everything downstream. For a well-established Cisco-only enterprise with existing DMVPN or SD-WAN, EIGRP — because it converges faster natively and I can use unequal-cost load balancing. In both cases I’d run BFD on top so my sub-second convergence numbers actually mean sub-second.”

That answer signals: you understand the trade-off, you know the ecosystem, and you think about convergence tuning.

Common exam traps

1. Confusing OSPF and EIGRP AD. OSPF = 110. EIGRP internal = 90 (better). EIGRP external = 170 (worse than OSPF). If BOTH are running on the same router, EIGRP internal wins by default.

2. Metric calculation on the exam. OSPF cost = 10^8 / bandwidth. Default reference bandwidth is 100 Mbps, so anything at or above 100 Mbps is cost 1 (bad in modern networks). Change with auto-cost reference-bandwidth 10000 to make it useful.

3. EIGRP K-values MUST match. If two EIGRP routers have different K-values, no adjacency. Same for OSPF area IDs.

4. DR/BDR only on broadcast networks. OSPF on point-to-point doesn’t elect a DR. The exam loves this.

5. EIGRP uses ports? No — direct IP protocol 88. OSPF uses direct IP protocol 89. Neither uses TCP or UDP.

Cheat strip

Query	OSPF	EIGRP
Convergence out of the box	5-40 s	Sub-second
Multi-vendor	Yes	Cisco only
Load balancing	Equal-cost	Equal + unequal (variance)
Neighbor state to know for the exam	FULL (after EXCHANGE + LOADING)	Passive (route stable) vs Active (recomputing)
Metric	Cost from BW	Composite (BW + delay by default)
Cost (interior)	110	90
Interior gateway of choice in US greenfield (2026)	OSPF	Legacy Cisco only

What to actually do

If you’re studying CCNA: deep-dive OSPF, understand EIGRP fundamentals well enough to recognize its behavior in show output. That matches the exam weight.

If you’re job hunting: be ready to name which is running at their environment and give a coherent one-minute answer on why you’d pick each. Recruiters trip up unprepared candidates on this.

If you’re setting up a lab: run BOTH. Configure the same 4-router topology first with OSPF, then flush and configure with EIGRP. Watch the neighbor states, look at the routing tables, kill a link and time the convergence. That drill is worth 10 read-throughs of a textbook.