Routing Technologies
Characteristics of routing technologies
What you will learn
- Distinguish static from dynamic routing.
- Explain administrative distance's role in choosing the best source.
- Explain metric's role in choosing the best path from the same source.
- Distinguish distance-vector from link-state protocols by convergence speed.
A router may learn several routes to the same destination network from different sources — a manual static entry, or a dynamic routing protocol like OSPF or RIP. It needs a clear criterion to pick exactly one route to add to its actual routing table, not every available route.
Static vs. Dynamic routing
| Static | Dynamic | |
|---|---|---|
| Configuration | Fully manual, set by the admin | Learned automatically by the router via a protocol |
| Response to network change | Doesn't adapt — needs manual editing | Adapts automatically when topology changes |
| Common use | Small networks or one specific backup route | Medium-to-large, changing networks |
Core concepts
| Administrative Distance | A number expressing trust in the route's source (static is usually lower than any dynamic protocol) — compared first between different sources. |
|---|---|
| Metric | An internal value specific to one protocol (hop count in RIP, cost in OSPF) — used only when administrative distance ties. |
| Default Route | The route used when no more specific route matches the destination — usually 0.0.0.0/0. |
Distance-vector vs. link-state
| Distance-vector (e.g., RIP) | Link-state (e.g., OSPF) | |
|---|---|---|
| Information exchanged | Shares the full routing table with direct neighbors only | Shares the state of every link across the whole network |
| Convergence speed | Slower — relies on periodic updates | Faster — reacts as soon as any link changes |
| Metric used | Hop count | Cost, tied to link speed |
The order never flips
Different sources are compared first via administrative distance (lowest wins), and the metric is only consulted when the source itself ties (the same protocol) — a common exam mistake is mixing up when each applies.
Quick check
Answer in your head first, then reveal.
What is compared first between two different routing sources?Reveal the answer
Administrative distance — the lowest wins.
When is the metric used?Reveal the answer
Only when administrative distance ties, i.e., from the same routing source.
What's the key difference between distance-vector and link-state in convergence speed?Reveal the answer
Link-state converges faster because it reacts immediately to any link change, unlike distance-vector, which relies on periodic updates.
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Sources
Used to verify the facts. The writing is original to Passuit.