What this topic covers
5 subtopics- Link state13
- Protocols11
- Distance vector10
- Basics6
- Modern routing5
- Beginner 15
- Intermediate 15
- Advanced 15
About this topic
Routers fill their forwarding tables using routing algorithms: link-state routers (OSPF) each run Dijkstra on a full map of the network, while distance-vector routers (RIP) repeatedly exchange their best-known distances with neighbours. Questions here use drawn networks; every distance, next hop and table entry was computed by running the algorithm (Dijkstra ties broken alphabetically).
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Sample questions
Try each one first, then open the answer for the explanation and why the other options are wrong.
What is the least-cost distance from u to z?
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
u → x (1) → y (1) → z (2) = 4. Going via w costs at least 3 + 5 = 8.
Running Dijkstra from u (ties broken alphabetically), in which order are nodes added to the set of finalised nodes?
Show answer and explanation
Explanation
Distances: x 1; then v 2 and y 2 tie (v first alphabetically); w 3 (via y); z 4. Many textbooks break the tie differently (y before v) – check the stated rule.
Why the other options are wrong
- Bx (1) is closer than v (2).
- Cv is at distance 2, not last.
- DValid with the other tie rule, not this one.
After the distance vectors converge, what is z's distance vector (to x, y, z)?
Show answer and explanation
Explanation
z reaches y directly (1) and x via y (1 + 2 = 3), never using the cost-7 link.
Why the other options are wrong
- Ax is 3 away.
- CThe direct link is not the best.
- Dy is 1 away.