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Routing Protocol Types Compared: RIP, OSPF, EIGRP, and IS-IS

Routers don't come pre-loaded with a map of the internet β€” they build one by talking to each other. Here's how the main routing protocols go about it.

What a routing protocol actually does

A routing protocol lets routers automatically exchange information about which networks they can reach and how, so administrators don't have to hand-type every path (a "static route") into every router. Routers recalculate automatically when a link goes down.

RIP: the simplest, and mostly retired

The Routing Information Protocol counts hops (the number of routers a packet crosses) and always prefers the path with the fewest hops, ignoring speed or congestion. It's simple to configure but scales poorly and is considered obsolete for anything beyond very small or classroom networks.

OSPF: link-state and fast to react

Open Shortest Path First gives every router a full map of the network (a link-state database) and calculates the best path itself, rather than trusting hop counts. It reacts quickly to outages and is one of the most widely used interior protocols today, especially in enterprise networks.

EIGRP: Cisco's hybrid approach

Enhanced Interior Gateway Routing Protocol blends distance-vector simplicity with link-state-like fast convergence, using a metric that factors in bandwidth and delay rather than just hop count. It was Cisco-proprietary for years before being partially opened, so it's mostly seen on Cisco-heavy networks.

IS-IS: OSPF's less visible cousin

Intermediate System to Intermediate System works similarly to OSPF β€” link-state, fast convergence β€” but runs a layer lower in the network stack and is protocol-agnostic. It's less common on typical enterprise networks but is a mainstay inside large ISP backbones.

All of these are interior protocols; BGP is different

RIP, OSPF, EIGRP, and IS-IS are all Interior Gateway Protocols (IGPs), designed to route traffic within a single organization's network. The Border Gateway Protocol (BGP) is an Exterior Gateway Protocol that routes traffic between separate networks (autonomous systems) across the internet β€” the two operate at completely different scales.

Why not just use one protocol everywhere?

Each protocol trades off differently between simplicity, speed of convergence, scalability, and vendor support. A small office might run nothing more complex than static routes or RIP, a mid-size enterprise typically runs OSPF or EIGRP, and an ISP backbone connecting thousands of routers usually runs IS-IS internally and BGP at its edges to talk to other networks.

Convergence time is the real differentiator

The property administrators care about most in practice is convergence time β€” how fast the network's routers agree on a new best path after a link fails. Older distance-vector protocols like RIP can take minutes; link-state protocols like OSPF and IS-IS typically converge in seconds, which is why they've largely replaced RIP outside of legacy and teaching environments.

Frequently Asked Questions

Do I need to know this to run a home network?

No β€” home routers use pre-programmed default routes and don't run these protocols at all. This is a concept from enterprise and ISP-scale networking, where multiple routers need to coordinate automatically.

Which protocol is "best"?

There isn't a universal best; the right choice depends on network size, vendor mix, and how fast the network needs to recover from a failure. OSPF is the most common general-purpose choice today, with IS-IS dominant inside large ISP cores and BGP handling everything between separate networks.