OSPF — end of module

What this checks. That you can explain how every router arrives at the same answer without anybody being in charge. You need 3 of 4 to pass, and every option is explained afterwards — including the ones you did not pick.

1. 1/4Two paths reach the same network, both two router hops. The northern path costs 10 + 10 and the southern 5 + 5. Which does OSPF install, and why?

   Work out a value

   The southern one, because 10 is less than 20 — hop count is not part of the calculation

   Neither — they tie on hop count, so traffic is load balanced

   The northern one, because higher cost means higher capacity
2. 2/4What does a Router-LSA describe?

   Tell two ideas apart

   Only the links of the router that originated it

   The whole topology as that router currently understands it

   The routes the router has installed
3. 3/4Two directly connected routers both send hellos forever, neither reports an error, and the adjacency never forms. What should you check first?

   Diagnose a failure

   Whether the hello and dead intervals match on both sides

   Whether the link is up

   Whether the routers' costs differ
4. 4/4An operator wants traffic to stop using a link without taking it out of service. What does OSPF offer?

   Apply it somewhere new

   Raise the interface's cost — the link stays up and advertised, and everyone's arithmetic comes out differently

   Configure a static route around it on every router

   Shut the interface down and bring it back when needed