Routing protocols help routers learn about remote networks and choose a path for forwarding traffic. The main difference between routing protocols is how they exchange route information, calculate the best path, react to network changes, and scale as the network grows.
If you are preparing for the CCNA exam, use this guide to review the concepts and then practise interpreting routes and OSPF behavior in a lab. For additional practice, see the 200-301 CCNA Premium PDF with the latest available questions and answers.
What Is a Routing Protocol?
A routing protocol is a set of rules that routers use to share reachability information. A router places the best learned routes in its routing table and uses that table when forwarding packets. Routing protocols should not be confused with routed protocols such as IPv4 and IPv6, which carry user data across the network.
Main Types of Routing Protocols
| Protocol type | How it works | Common example | Main consideration |
|---|---|---|---|
| Distance vector | Shares route and distance information with neighboring routers | RIP | Simple, but slower convergence and limited scale |
| Advanced distance vector | Uses neighbor relationships and multiple metrics | EIGRP | Fast convergence with Cisco-focused terminology |
| Link state | Builds a topology database and calculates the shortest path | OSPF, IS-IS | Scales well but requires more planning |
| Path vector | Advertises network paths and policy attributes between autonomous systems | BGP | Designed for large-scale, policy-based routing |
Distance-vector protocols
Distance-vector protocols learn routes from directly connected neighbors. They select a route using a distance measurement such as hop count. RIP is the best-known example: it uses hop count as its metric and supports a maximum usable path of 15 hops. Its simple operation makes it useful for learning, but it is not normally chosen for large modern networks.
Advanced distance-vector protocols
EIGRP is often described as an advanced distance-vector protocol. It forms neighbor relationships, keeps a topology table, and uses the Diffusing Update Algorithm to find loop-free routes. Its composite metric considers bandwidth and delay by default. Candidates should understand its terminology even when the exam places greater configuration emphasis on OSPF.
Link-state protocols
Link-state protocols advertise information about links rather than sending an entire routing table at every regular update. Routers use this information to build a shared view of the topology. OSPF runs the shortest path first algorithm and uses cost as its metric. It supports hierarchical design through areas, which improves scalability and limits the effect of topology changes.
Path-vector protocols
BGP is used to exchange routes between autonomous systems. It makes decisions using path attributes and routing policy, not simply the shortest technical path. This gives network operators control over how traffic enters and leaves their networks. BGP is essential to Internet routing, but its goals differ from those of interior gateway protocols used within one organization.
Key Differences Between Routing Protocols
Metric
A metric is the value a routing protocol uses to compare paths that it learned through that same protocol. RIP uses hop count, OSPF uses cost, and EIGRP uses a composite metric. BGP uses a decision process based on multiple path attributes.
Administrative distance
Administrative distance is different from a metric. A router uses administrative distance to choose between routes learned from different sources. The route with the lower administrative distance is normally preferred. The metric is then used to compare routes learned by the same routing protocol.
Convergence
Convergence is the time required for routers to agree on the network topology after a change. Faster convergence reduces disruption when a link fails. Link-state and advanced distance-vector protocols generally converge faster than traditional distance-vector protocols, provided they are designed and configured correctly.
Updates and resource use
Protocols also differ in how much bandwidth, CPU, and memory they use. Periodic full updates are simple but can be inefficient. Triggered or incremental updates reduce unnecessary traffic, while topology databases provide more detail at the cost of additional memory and processing.
Scale and design
RIP is suitable mainly for small, simple environments. OSPF can support larger enterprise networks through its area design. EIGRP can also converge quickly in enterprise environments. BGP is the appropriate choice when policy and routing between autonomous systems are required.
Routing Protocols in CCNA Preparation
The current CCNA objectives include interpreting routing-table entries and configuring single-area OSPF for IPv4 and IPv6. Focus on route source codes, prefixes, next hops, administrative distance, metrics, neighbor formation, router IDs, and DR/BDR behavior. Verify the current scope in the official Cisco 200-301 exam topics.
A productive study sequence is to learn the concept, build a small lab, inspect the routing table, and then answer scenario-based questions. You can also review our Cisco CCNA notes for related topics.
Quick Review
- RIP: distance vector; selects routes by hop count.
- EIGRP: advanced distance vector; uses a composite metric and DUAL.
- OSPF: link state; calculates routes using cost and supports areas.
- BGP: path vector; selects routes using attributes and policy.
- Administrative distance: compares routes from different sources.
- Metric: compares paths learned by the same routing protocol.
For structured revision after studying the concepts, review the Cisco 200-301 Premium PDF. It provides the latest available questions and answers for focused practice. Use it with hands-on labs and official Cisco learning material.
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