CCNA 3 v6.0 (Scaling Networks v6) Chapter 7: EIGRP Tuning and Troubleshooting: Check Your Understanding Questions Answers
1. What is the purpose of a Null0 route in the routing table?
- To act as a gateway of last resort
- To prevent routing loops when summarizing routes
- To prevent the router from sending EIGRP packets
- To redistribute external routes into EIGRP
Explanation: EIGRP for IPv4 automatically installs a Null0 summary route into the routing table when EIGRP automatic summarization is enabled and there is at least one EIGRP learned subnet. Null0 is a virtual interface that is a route to nowhere and is used to prevent routing loops for destinations that are included in a summary network but do not have a specific entry in the routing table.
2. Which administrative distance is used to advertise routes learned from other protocols that are redistributed into EIGRP?
Explanation: Routes learned from other routing protocols that are redistributed into EIGRP are known as external routes and are assigned an administrative distance of 170.
3. Which command would limit the amount of bandwidth that is used by EIGRP for protocol control traffic to approximately 128 Kbps on a 1.544 Mbps link?
- ip bandwidth-percent eigrp 100 8
- maximum-paths 8
- traffic-share balanced
- variance 8
Explanation: The amount of bandwidth that EIGRP uses by default for control traffic is 50 percent of the bandwidth of the exit interface. To change this default setting, you use the ip bandwidth-percent eigrp command. The ip bandwidth-percent eigrp 100 8 command sets the bandwidth for autonomous system 100 at 8 percent of the bandwidth of the interface.
4. By default, how many equal-cost routes to the same destination network will EIGRP install in the routing table?
Explanation: For load balancing, EIGRP by default installs up to four equal-cost paths to the same destination network in the routing table.
5. Which EIGRP parameter must match between all routers forming an EIGRP adjacency?
- Administrative distance
- Autonomous system number
- Hello timer
- Hold timer
Explanation: EIGRP routers must belong to the same autonomous system for an adjacency to be successful. The autonomous system number is specified at the end of the router command.
6. In which scenario will the use of EIGRP automatic summarization cause inconsistent routing in a network?
- When the routers in an IPv4 network are connected to discontiguous networks with automatic summarization enabled
- When the routers in an IPv4 network have mismatching EIGRP AS numbers
- When there is no adjacency that is established between neighboring routers
- When there is no common subnet that exists between neighboring routers
Explanation: If there are discontiguous IPv4 networks, automatic summarization causes inconsistent routing because routes are summarized at classful boundaries. When there is no common subnet between EIGRP neighbors, an adjacency cannot form. Mismatching EIGRP AS numbers and the lack of an adjacency will not cause inconsistent routing but a lack of routing overall.
7. Which command can be issued on a router to verify that automatic summarization is enabled?
- show ip eigrp interfaces
- show ip eigrp neighbors
- show ip interface brief
- show ip protocols
Explanation: To verify whether automatic summarization is being performed on a router, enter the show ip protocols command. The show ip eigrp interfaces command shows which interfaces are enabled for EIGRP. The show ip interface brief command is used to verify that the status and protocol are both up for an interface connected to a router. The show ip eigrp neighbors command on a router verifies the establishment of EIGRP neighbor adjacencies with other routers.
8. Which address is used by an IPv6 EIGRP router as the source for hello messages?
- The 32-bit router ID
- The all-EIGRP-routers multicast address
- The interface IPv6 link-local address
- The IPv6 global unicast address that is configured on the interface
Explanation: EIGRP for IPv6 uses the link-local address of the router exit interface as the source address for EIGRP messages, including hello messages.
9. When will a router that is running EIGRP put a destination network in the active state?
- When the connection to the successor of the destination network fails and there is no feasible successor available
- When the EIGRP domain is converged
- When there is an EIGRP message from the successor of the destination network
- When there is outgoing traffic toward the destination network
Explanation: If the connection to the successor of a network is lost and there is no feasible successor in the topology database, DUAL puts the network into the active state and actively queries the neighbors for a new successor. In a normal circumstance when the network is reachable and traffic is normal, the network is put into passive mode.
10. Which two parameters does EIGRP use by default to calculate the best path? (Choose two.)
- Transmit and receive load
Explanation: EIGRP uses a composite metric. By default, EIGRP uses the slowest bandwidth of all interfaces between the source and the destination and the sum of all interface delays along the path to calculate the best path. The worst reliability and the worst load on a link between source and destination can also be used to select the best path, but these are not default metric values. MTU is included in routing updates but is not used as a routing metric.
11. A network administrator wants to verify the default delay values for the interfaces on an EIGRP-enabled router. Which command will display these values?
- show interfaces
- show ip protocols
- show ip route
- show running-config
Explanation: The show interfaces command is used to show the delay, in microseconds, of a specified interface. This command also provides the default delay value or an administratively configured value. The show running-config command displays only an administratively configured value. The commands show ip route and show ip protocols do not provide the delay value of each interface.
12. An administrator issues the router eigrp 100 command on a router. What is the number 100 used for?
- The autonomous system number
- The length of time this router will wait to hear hello packets from a neighbor
- The maximum bandwidth of the fastest interface on the router
- The number of neighbors supported by this router
Explanation: The router eigrp 100 command uses the number as a process ID to keep track of the running instance of the EIGRP process, as several EIGRP processes can be run at the same time. This number is called the autonomous system number.