Computer Network & Network Security System — Network Layer, NEC licence examination syllabus (Nepal Engineering Council).
Three protocols, because they answer three different questions — inside a small network, inside a large one, and between organisations that do not trust each other.
The three are not competitors at the same job. Knowing which problem each was built for explains every difference in their design, and that is what an examiner is testing when they ask you to compare them.
AlgorithmDistance vector — Bellman-Ford style. Each router knows only its neighbours and what they advertise.
MetricHop count. Every link counts as 1, regardless of speed.
LimitA maximum hop count, beyond which a destination is treated as unreachable.
UpdatesThe whole table, sent to neighbours periodically.
Counting hops rather than capacity is RIP's defining weakness: a two-hop path over slow links beats a three-hop path over fast ones, every time. The hop limit exists to make count-to-infinity terminate, as the algorithms chapter sets out — it is a safety mechanism, not a statement about network size.
AlgorithmLink state. Every router floods a description of its own links, so all of them build the same map and run Dijkstra on it.
MetricCost, derived from bandwidth — a fast link costs less than a slow one.
AreasThe network is divided into areas, and detail is summarised at the boundaries.
UpdatesTriggered by change, not by a timer, and only the change is sent.
AlgorithmPath vector — advertises the full list of autonomous systems a route passes through, not just a cost.
ScopeBetween autonomous systems, where RIP and OSPF work within one.
Decides byPolicy as much as by distance — business relationships, not only path length.
Carrying the whole path solves two problems at once. A router seeing its own network in an advertised path knows immediately that accepting it would create a loop — no counting required. And an operator can refuse a route for reasons that have nothing to do with efficiency, which is what "policy" means here: the shortest path is often not the one anyone wants to use.
Everything above routes unicast traffic — one sender, one receiver. Multicast delivers one sender's traffic to a group of receivers without sending a separate copy to each, which needs routers to build a distribution tree rather than a path. The saving is real for live video and similar traffic, where the alternative is one identical stream per viewer across shared links.
RIP's hop limit and network size. The limit terminates count-to-infinity. It is not a claim that larger networks cannot exist.
OSPF areas and subnets. Areas are a routing-protocol structure for containing updates. Subnets are an addressing structure. They often align, and they are not the same thing.
Interior and exterior protocols. The dividing line is administrative control, not size.
RIP — distance vector, hop count, hop-limited, periodic full-table updates.
OSPF — link state, bandwidth-based cost, areas to contain updates, triggered partial updates.
BGP — path vector, between autonomous systems, decides by policy, detects loops by reading the path.
Interior versus exterior is about trust and control, not about how big the network is.
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