OSPF vs EIGRP: What's the Difference?
The core difference is how each protocol figures out the best path. OSPF is a link-state protocol: every router floods information about its own links, so all routers in an area build an identical map of the network and each runs the SPF (Dijkstra) algorithm to calculate its own shortest paths. EIGRP is an advanced distance-vector protocol: routers learn routes from their directly connected neighbors and run DUAL to select the best path plus a pre-computed loop-free backup. OSPF's metric is cost (derived from bandwidth) with an administrative distance of 110; EIGRP uses a composite metric (bandwidth and delay by default) with an administrative distance of 90 for internal routes.
Part of the OSPF learning hub
The other big difference is ownership and scope. OSPF is an open standard (RFC 2328) that runs on any vendor's equipment, while EIGRP originated at Cisco and is now published as informational RFC 7868 but is realistically deployed Cisco-to-Cisco. One practical note for exam-takers: OSPFv2 is on the CCNA 200-301 blueprint, but EIGRP is CCNP-level and is not on the CCNA exam.
| At a glance | OSPF | EIGRP |
|---|---|---|
| Protocol type | Link-state | Advanced distance-vector |
| Standard / vendor | Open standard (RFC 2328), any vendor | Cisco-originated, now open (RFC 7868) |
| Metric | Cost, derived from bandwidth | Composite: bandwidth + delay (by default) |
| Administrative distance | 110 | 90 (internal routes) |
| Algorithm | SPF / Dijkstra | DUAL (Diffusing Update Algorithm) |
| Structure / design | Hierarchical areas; DR/BDR on shared segments | AS number; feasible successors; flat with summarization |
| Backup path / convergence | Re-runs SPF on a topology change | Instant failover to a feasible successor when one exists |
| CCNA 200-301 blueprint | On the exam (OSPFv2) | Not on the exam (CCNP-level) |
What OSPF is
OSPF (Open Shortest Path First) is a link-state interior gateway protocol defined in RFC 2328. Every router advertises its links, so all routers in an area build an identical link-state database — a full map of the topology — then each independently runs the SPF/Dijkstra algorithm to compute its own shortest-path tree.
Its metric is cost, calculated from interface bandwidth, where a lower cost is preferred. OSPF scales through a hierarchy of areas anchored on the backbone (area 0), and on broadcast/multiaccess segments it elects a DR and BDR to reduce flooding. Its administrative distance is 110. OSPFv2 is part of the CCNA 200-301 blueprint.
What EIGRP is
EIGRP (Enhanced Interior Gateway Routing Protocol) is Cisco's advanced distance-vector protocol — originally proprietary, now published as informational RFC 7868. Routers exchange routes only with directly connected neighbors (the distance-vector part), but run DUAL to guarantee a loop-free best path, called the successor, and, when the math allows, a pre-computed loop-free backup called the feasible successor.
Its metric is composite: by default it uses bandwidth and delay (load and reliability can be added but are off by default). Neighbors must share the same autonomous system (AS) number to form an adjacency. Its administrative distance is 90 for internal routes. EIGRP is CCNP-level material and is not on the CCNA 200-301 exam.
The key differences explained
How they think: OSPF builds a complete topology map and calculates paths itself; EIGRP trusts its neighbors' advertised distances and layers its own DUAL loop-prevention logic on top.
Metric: OSPF's cost is bandwidth-based only, while EIGRP's default composite of bandwidth plus delay can prefer a different path across the very same links.
Convergence: both are fast, but EIGRP can install a feasible successor instantly on failure without recalculating; OSPF must re-run SPF. When EIGRP has no feasible successor it goes 'active' and queries neighbors, which can be slower.
Administrative distance: if a Cisco router ever learned the same route from both, EIGRP's AD of 90 beats OSPF's 110, so the EIGRP route would win.
Vendor: OSPF runs on any vendor's gear; EIGRP is realistically Cisco-to-Cisco.
When to choose each
Choose OSPF for multi-vendor networks, when an open standard is required, or when a clean hierarchical area design fits — and it is what you will be tested on for CCNA.
Choose EIGRP in an all-Cisco environment that wants simple configuration, very fast convergence through feasible successors, and unequal-cost load balancing (something OSPF does not do).
In practice the deciding factor is usually the vendor mix: mixed vendors point to OSPF, while an all-Cisco shop can use either — often EIGRP for its simplicity.
A common gotcha
EIGRP's classic trap is the AS number: the value in 'router eigrp X' must match on both neighbors or the adjacency never forms. It is not a globally significant number — just a local grouping that both ends must agree on.
OSPF's classic trap is its bandwidth-based cost. The default reference bandwidth is 100 Mbps, so every interface at or above 100 Mbps (FastEthernet, Gigabit, 10-Gig) gets the same cost of 1 unless you raise the reference bandwidth — and you must raise it consistently on every router, or path selection becomes inconsistent.
Frequently asked questions
Which is better, OSPF or EIGRP?
Neither is universally better. EIGRP tends to converge faster thanks to pre-computed feasible successors, is simpler to configure, and supports unequal-cost load balancing — but it is realistically Cisco-only. OSPF is an open standard that works across vendors and scales cleanly with areas. For a multi-vendor network, OSPF is the safer choice; for an all-Cisco network that wants simplicity and fast failover, EIGRP is a strong option.
When would I use each?
Use OSPF when you have mixed vendors, need a standards-based protocol, or are studying for CCNA (OSPFv2 is on the 200-301 exam). Use EIGRP in an all-Cisco environment that benefits from its fast convergence and easy setup — but remember it is CCNP-level material and is not tested on CCNA.
What's the main difference?
OSPF is link-state: every router builds a full map of the network and runs SPF/Dijkstra to compute paths, using a bandwidth-based cost metric and administrative distance 110. EIGRP is advanced distance-vector: routers learn from neighbors and use DUAL with feasible successors, a composite bandwidth-plus-delay metric, and administrative distance 90. On top of that, OSPF is open and multi-vendor, while EIGRP is Cisco-originated (now RFC 7868).
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