How a Router Picks the Path

In the picture

1. 1The packet: a piece of data travelling from the laptop to the server
2. 2The first router: it compares the routes and decides where to send the packet next
3. 3A fast, thick link: low OSPF cost, so the longer upper route costs less in total
4. 4A slow, thin link: high OSPF cost, but RIP would pick this route because it has fewer hops

Examples

• A sat-nav that sends you along a longer motorway instead of the shorter route through slow town streets
• A video call travelling through several fast fibre links instead of one slow, congested connection

Quiz: How a Router Picks the Path (Age 18)

1. 1

   How does OSPF decide which path a packet should take?

   • It picks the path that passes through the fewest routers
   • It picks the path that the previous packet used
   • It picks the path with the lowest total link cost
2. 2

   Under RIP, how is a destination treated if reaching it would take more than 15 hops?

   • As the preferred route, as long as its links are fast
   • As reachable, but only with a higher link cost
   • As unreachable
3. 3

   One route crosses more routers but uses fast links, and another crosses fewer routers but includes a slow link. Which statement is correct?

   • RIP will choose the route with fewer hops, even though it includes the slow link
   • RIP will choose the route with fast links, because it has the lower cost
   • OSPF and RIP will always choose the same route

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.