What is RIP (Routing Information Protocol)?
Learn what RIP is, how hop-count distance-vector routing works, its 16-hop limit, and why OSPF replaced it — interview Q&A.
Expected Interview Answer
RIP (Routing Information Protocol) is one of the oldest distance-vector routing protocols, used by routers to share reachability information within an autonomous system by counting hops, where a route is considered unreachable once its hop count reaches 16.
Each RIP router periodically broadcasts (or multicasts, in RIPv2) its entire routing table to directly connected neighbors, and every neighbor merges that information into its own table, incrementing the hop count by one for each router along the path. Because it only considers hop count, RIP has no concept of bandwidth or latency, so it can pick a slow satellite link with two hops over a fast fiber link with three hops, which is a core limitation compared to more modern protocols like OSPF that use link-cost metrics. RIP also converges slowly after a topology change, since routers rely on periodic full-table broadcasts (typically every 30 seconds) rather than event-driven updates, and it uses mechanisms like split horizon, route poisoning, and holddown timers to fight routing loops, though these still leave it far behind link-state protocols in convergence speed. Its 16-hop limit means RIP is only practical for small networks; it has been largely superseded in production by OSPF and BGP, but interviewers still use it as the simplest concrete example of a distance-vector protocol.
- Simple to configure, good teaching example of distance-vector routing
- Adequate for small, flat networks with few hops
- Loop-mitigation techniques like split horizon reduce (not eliminate) loops
- Illustrates the tradeoffs that motivated link-state protocols like OSPF
AI Mentor Explanation
RIP is like a fielding captain choosing where to throw the ball by only counting how many relays it takes to reach the keeper, never considering whether a fielder has a weak arm or the ground is muddy on that side. A three-throw relay through fast, accurate fielders gets rejected in favor of a two-throw relay through a slower, error-prone one, purely because it has fewer hops. This blind hop-counting, ignoring actual throw quality, is exactly RIP’s core weakness compared to metric-aware routing protocols.
Step-by-Step Explanation
Step 1
Table exchange
Each RIP router periodically broadcasts or multicasts its full routing table to directly connected neighbors.
Step 2
Hop counting
A receiving router increments the hop count by one for each learned route and updates its own table if it finds a better path.
Step 3
Loop mitigation
Techniques like split horizon and route poisoning are applied to reduce routing loops from stale information.
Step 4
Unreachable threshold
A route with a hop count of 16 is marked unreachable/infinite, capping RIP's usable network diameter.
What Interviewer Expects
- Correctly classifies RIP as a distance-vector protocol using hop count
- States the 16-hop limit and its implication for network size
- Explains RIP ignores bandwidth/latency, unlike link-state protocols
- Mentions slow convergence and loop-mitigation techniques like split horizon
Common Mistakes
- Confusing RIP with a link-state protocol like OSPF
- Not knowing the 16-hop limit exists or what it means
- Assuming RIP considers bandwidth when it only counts hops
- Forgetting that RIP converges slowly due to periodic full-table broadcasts
Best Answer (HR Friendly)
“RIP is one of the earliest and simplest protocols routers used to figure out the best path to send data, and it does that purely by counting how many routers a path passes through — fewer hops wins, even if a longer path would actually be faster. That simplicity made it easy to set up but also its biggest weakness, which is why more modern networks use smarter protocols like OSPF instead.”
Code Example
# View routes learned via RIP (using FRRouting’s ripd)
vtysh -c "show ip rip"
# Example output:
# Network Next Hop Metric From
# 10.1.0.0/24 10.0.0.2 2 RIP
# 10.2.0.0/24 10.0.0.2 3 RIP
# Show the kernel routing table to confirm installed routes
ip route showFollow-up Questions
- Why is RIP limited to a 16-hop network diameter?
- How does split horizon help prevent routing loops in RIP?
- What are the practical differences between RIP and OSPF?
- What is the difference between RIPv1 and RIPv2?
MCQ Practice
1. What metric does RIP use to select the best route?
RIP is a distance-vector protocol that selects routes purely based on the number of hops.
2. What hop count does RIP treat as unreachable?
RIP treats a hop count of 16 as infinite/unreachable, capping the usable network diameter.
3. What is a key limitation of RIP compared to OSPF?
RIP relies purely on hop count and periodic full-table broadcasts, making it slower to converge and blind to link quality compared to link-state protocols like OSPF.
Flash Cards
What is RIP? — A distance-vector routing protocol that selects paths based purely on hop count.
RIP's hop limit? — 16 hops is treated as unreachable/infinite.
RIP's main weakness? — It ignores bandwidth/latency and converges slowly via periodic full-table broadcasts.
What replaced RIP in most networks? — Link-state protocols like OSPF, and BGP for inter-domain routing.