RIP
Distance-vector routing: hop-count metric (16 means infinity), updates every 30 seconds, the update rule, count to infinity and its remedies (split horizon, poisoning, triggered updates), RIPv1 against RIPv2.
- 30 cards
- 6 topics
- Free
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Each topic is weighted the way the exam weighs it.
- Concepts
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- The numbers
- Scenarios
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A few cards from the deck
RIP: what is it?
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An interior distance-vector routing protocol: each router sends its whole table to its neighbours every 30 seconds, over UDP port 520, and measures distance in hops.
The metric ignores bandwidth: two 10 Mb/s links beat three 1 Gb/s links. Beyond 15 hops, the destination is considered unreachable, which restricts RIP to small networks.
R1 has a route to network N at 3 hops via R3. Its neighbour R2 announces N at 1 hop. What does R1 do?
- It replaces its route: N at 2 hops via R2
- It keeps N at 3 hops via R3, as an installed route is never replaced
- It replaces its route: N at 1 hop via R2
- It keeps both routes and shares the traffic between R2 and R3
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It replaces its route: N at 2 hops via R2
The distance via R2 is 1 + 1 = 2, better than 3: the route is replaced. R1 cannot be 1 hop from N, since R2 sits in between. Load sharing only exists for routes with equal metrics.
In RIP, a route with metric … is unreachable, and each router sends its table every … seconds.
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In RIP, a route with metric 16 is unreachable, and each router sends its table every 30 seconds.
The longest usable path is therefore 15 hops. The 30 seconds is the update period, not a failure delay.
Distance vector: what is it?
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A family of algorithms where each router knows, for each destination, only a distance and a next neighbour, and learns them solely from the lists its neighbours send it.
A router never sees the map of the network, only what its neighbours say about it: it is routing by hearsay, hence count to infinity. Link state, by contrast, gives every router the whole map.