CCNA Quiz - Dynamic Routing

1. Which of the following is not a routing protocol? A. EIGRP B. BGP C. IPv4 D. IS-IS E. OSPF

(1) C (IPv4) Explanation: All of the choices are different routing protocols except IPv4 -which is a routed protocol

2. Which of the protocols below is the most popular routing protocol used in the backbone of the Internet? A. OSPF B. IS-IS C. RIP D. BGP

(2) D (BGP) Explanation: Because they are in charge of different autonomous systems, service providers use exterior gateway protocols to exchange routes on the Internet. BGP is the primary protocol used for routing in the backbone of the internet

3. ___________________are used to share routes between autonomous systems: A. Exterior Gateway Protocols B. Interior Gateway Protocols C. Service Provider Protocols D. Gateway Resolution Protocols

(3) A (Exterior Gateway Protocols) Explanation: Exterior Gateway Protocols such as BGP, for instance, are used to advertise routes between different autonomous systems. Interior gateway protocols are used to share routes within the same autonomous system (OSPF, EIGRP, RIP). The last two answers are bogus protocols.

4. You have been given access to a large lab with many routers to use. For experimental purposes, you have decided to configure OSPF, RIP and EIGRP routing simultaneously on each router in the network. Router-A is has learned three routes to the 172.16.31.0 /24 subnet - one from each routing protocol. Which routing protocol will be selected to route packets to the 172.16.31.0 /24 subnet? A. OSPF B. EIGRP C. RIP D. The router will load balance between each of the routes in a round-robin fashion

(4) B (EIGRP) Explanation: This is a good example for comparison sake . . . . in reality, you will probably go a lifetime without experiencing a network that is running these three protocols simultaneously. But, if you did . . . . then EIGRP would be the winner because it has the lowest administrative distance of the three protocols. EIGRP (90) OSPF (110) RIP (120)

5. The key components to the metric for an EIGRP route are: (choose two) A. Cost B. Delay C. Number of hops D. Bandwidth

(5) B, D (Delay, Bandwidth) Explanation: OSPF bases its metric on cost which is tied to the bandwidth of an interface. The formula for calculating an EIGRP metric includes several parameters. But, using the default values for variable parameters, the bandwidth and delay are used to calculate the metric

6. Which OSPF message type is used to establish and maintain neighbor adjacencies? A. Link-State Request (LSR) B. Link-State Update (LSU) C. Link-State Acknowledgement(LSA) D. Hello

(6) D (Hello) Explanation: The two main things that OSPF hellos are used for: 1. Discover OSPF neighbors - is there anybody out there? 2. Maintain neighbor adjacencies - hello, are you still there? As part of the process of negotiating the neighbor adjacency, the hellos also contain the parameters that must match between the two routers (area-id, ip subnet, MTU. Etc . . . .)

7. Which of the below are possible causes of routing loops? (Choose all that apply) A. Static Routes B. No TTL C. Reverse Route Advertisements D. Split Horizon

(7) A, C (Static Routes, Reverse Route Advertisements) Explanation: Static routes can easily create a routing loop by simply misconfiguring the routing statements so that two directly connected routers are pointing to each other to get to the same route. Reverse route advertisements, if allowed, could also create a routing loop. A reverse route advertisement is when I learn about a route from Neighbor A. I then immediately advertise the route back to neighbor A as if I was the source. The end result is that I have a route that points to neighbor A and neighbor A has a route that points to me. We will bounce any packet to that destination back and forth like a ping pong ball until the TTL field decrements to 0.

8. You have been shown a piece of the tracer oute output from aco-worker and asked to help identify what maybe wrong with connectivity to this ip address on the Internet? (Check on Module 6) A. The link between 192.168.2.1 and 172.16.24.2 is down B. There is a switching loop C. There is a routing loop D. BGP route reflection has been enabled

(8) C (there is a routing loop) Explanation: What the traceroute shows is a path that hits 192.168.2.1 and then to 172.16.24.2, but then goes back to 192.168.2.1 and continues to bounce in between these two addresses. This is the classic signature of a routing loop where two routers are playing "hot potato" with a packet.

9. Which of the following is not a method for preventing routing loops? A. Static Routes B. Split Horizon C. Route Poisoning D. Hold Down Timers E. Maximum Hop Count

(9) A (Static Routes) Explanation: Static routes, if configured incorrectly, can actually create routing loops, not prevent them. All of the other answers are measures that will prevent routing loops.