How Routers Pick a Path

In the picture

1. 1The packet: a small chunk of data with a destination address
2. 2A router: reads the address and forwards the packet to the next hop
3. 3A fast, high-bandwidth link: low cost, so OSPF sends the packet this way
4. 4A slow, low-bandwidth link: fewer hops, so RIP would pick this shorter route

Examples

• Your video call taking a longer but faster fibre route between cities instead of a short, congested one
• A GPS app choosing the motorway over a shorter road full of traffic lights

Quiz: How Routers Pick a Path (Age 17)

1. 1

   How does a distance-vector protocol like RIP decide which route a packet should take?

   • It picks the route with the fewest hops
   • It picks the route with the highest-bandwidth links
   • It picks the route with the lowest total link cost
2. 2

   What does a link-state protocol like OSPF do before it chooses a route?

   • It sends a copy of the packet down every link
   • It asks only the next router for directions
   • It builds a map of the whole network
3. 3

   Route A has 2 hops over slow, low-bandwidth links. Route B has 4 hops over fast, high-bandwidth links. Which route does OSPF choose?

   • Route A, because slow links have a lower cost
   • Route A, because it has fewer hops
   • Route B, because its fast links give a lower total cost

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.