CCNA FAQ: Routing Protocol Theory
Q1. Which of the following routing protocols are considered to use distance vector logic? (Choose two answers.)
f. Integrated IS-IS
Answer: A and B
Q2. Which of the following routing protocols are considered to use link-state logic? (Choose two answers.)
f. Integrated IS-IS
Answer: D and F
Q3. Which of the following routing protocols use a metric that is, by default, at least partially affected by link bandwidth? (Choose two answers.)
Answer: C and D
Q4. Which of the following interior routing protocols support VLSM? (Choose four answers.)
e. Integrated IS-IS
Answer: B, C, D, and E
Q5. Which of the following situations would cause a router using RIP-2 to remove all the routes learned from a particular neighboring router?
a. RIP keepalive failure
b. No longer receiving updates from that neighbor
c. Updates received 5 or more seconds after the last update was sent to that neighbor
d. Updates from that neighbor have the global “route bad” flag
Answer: B. Distance vector protocols rely on periodic full routing updates from their neighbors to confirm that the neighbor is still working.
Q6. Which of the following distance vector features prevents routing loops by causing the routing protocol to advertise only a subset of known routes, as opposed to the full routing table, under normal stable conditions?
a. Counting to infinity
b. Poison reverse
d. Split horizon
e. Route poisoning
Answer: D. Split horizon causes a router to not advertise routes out an interface if the route would cause packets to be sent out that same interface.
Q7. Which of the following distance vector features prevents routing loops by advertising an infinite metric route when a route fails?
b. Full updates
c. Split horizon
d. Route poisoning
Explanation: D. Route poisoning means advertising the failed route with an “infinite” metric, as opposed to simply ceasing to advertise the route. Poison reverse is route poisoning by advertising a route that previously was not advertised because of split horizon.
Q8. A router that is using a distance vector protocol just received a routing update that lists a route as having an infinite metric. The previous routing update from that neighbor listed a valid metric. Which of the following is not a normal reaction to this scenario?
a. Immediately send a partial update that includes a poison route for the failed route
b. Put the route into holddown state
c. Suspend split horizon for that route and send a poison reverse route
d. Send a full update listing a poison route for the failed route
Explanation: A. The router should not immediately send a full update. Instead, distance vector protocols immediately send a partial routing update, listing just the poisoned route.
Q9. An internetwork is using a link-state routing protocol. The routers have flooded all LSAs, and the network is stable. Which of the following describes what the routers will do to reflood the LSAs?
a. Each router refloods each LSA using a periodic timer that has a time similar to distance vector update timers.
b. Each router refloods each LSA using a periodic timer that is much longer than distance vector update timers.
c. The routers never reflood the LSAs as long as the LSAs do not change.
d. The routers reflood all LSAs whenever one LSA changes.
Answer: B. Link-state protocols reflood each LSA on a periodic but longer timer. With RIP, the update timer is 30 seconds, and with OSPF, the timer is 30 minutes.
Q10. Which of the following is true about how a router using a link-state routing protocol chooses the best route to reach a subnet?
a. The router finds the best route in the link-state database.
b. The router calculates the best route by running the SPF algorithm against the information in the link-state database.
c. The router compares the metrics listed for that subnet in the updates received from each neighbor and picks the best (lowest) metric route.
Explanation: B. Link-state protocols collect information about the internetwork in the form of LSAs, which sit in memory in the link-state database. The router then runs the SPF algorithm to calculate that router’s best metric route to reach each subnet.