Chapter 3: Quiz – Advanced EIGRP (Answers) CCNPv8 ENARSI

1. What is the default maximum amount of bandwidth that can be used for exchanging EIGRP messages on an EIGRP-configured interface?

  • 50%
  • 10%
  • 100%
  • 75%

Explanation: By default, EIGRP uses up to 50% of the configured bandwidth of an interface for EIGRP control information. On a 128 kbps link, this would mean that up to 64 kbps is used for EIGRP information.

2. If replies are not received from all outstanding queries, how long will an EIGRP router wait before placing a route into the SIA state?

  • 3 seconds
  • 60 seconds
  • 120 seconds
  • 180 seconds

Explanation: Occasionally, an EIGRP query is delayed. EIGRP maintains a timer (active timer), which has a default value of 180 seconds. EIGRP waits half of this timer for a reply. If the router does not receive a response within 90 seconds, the originating router sends a SIA query to EIGRP neighbors that did not respond. The router should respond within 90 seconds upon receipt of this query. If a router fails to respond before the active timer expires, the SIA state is declared for a neighbor.

3. What is the purpose of the EIGRP Null0 summary route?

  • to enhance security by hiding all internal networks that are included in a summary route
  • to prevent routing loops for destination networks which do not actually exist but are included in a summary route
  • to reduce bandwidth consumption for traffic that is leaving the network
  • to ensure that all traffic destined for individual subnets uses one single best path

Explanation: The Null0 interface represents a route to nowhere. Using a route to the Null0 interface prevents routing loops for any destination networks present in the summary route that do not actually exist.

4. A network student has to prepare a paper about EIGRP network summarization, but the student does not know much about summarization metrics. What piece of information is accurate about EIGRP summarization?

  • The summarizing router uses the highest metric of the component routes in the summary aggregate prefix.
  • The path metric for the summary aggregate is based on an average of the path attributes of the component routers.
  • Every time a matching component route for the summary aggregate is added or removed, downstream routes must run the DUAL again.
  • EIGRP path attributes are inserted into the summary route so that downstream routers can calculate the correct path metric for the summarized prefix.

Explanation: The summarizing router uses the lowest metric of the component routes in the summary aggregate prefix. The path metric for the summary aggregate is based on the path attributes of the path with the lowest metric. EIGRP path attributes such as total delay and minimum bandwidth are inserted into the summary route so that downstream routers can calculate the correct path metric for the summarized prefix.

5. Refer to the exibit. Both routers are configured to use the EIGRP routing protocol. The network administrator wants to enable manual summarization by issuing the displayed command. Where should the administrator apply this command?

Chapter 3: Quiz - Advanced EIGRP (Answers) CCNPv8 ENARSI 2

  • in router configuration mode after entering the router eigrp 100 command
  • in interface mode on the Gi0/1 interface of R1
  • in interface mode on the S0/0/0 interface of R1
  • in interface mode on the S0/0/0 interface of R2

Explanation: EIGRP summarizes network prefixes on an interface-by-interface basis. A summary aggregate is configured for the EIGRP interface. Without summarization, R1 advertises 192.168.10.0/24, 192.168.20.0/24, 192.168.30.0/24, and 192.168.40.0/24. R1 summarizes these network prefixes to the summary aggregate 192.168.0.0/16 prefix so that only one advertisement is sent to R2. Therefore, the command has to be applied to the serial0/0/0 interface of R1.

6. Which time interval is used by default to send EIGRP hello packets on low bandwidth interfaces?

  • 1 second
  • 5 seconds
  • 60 seconds
  • 30 seconds

Explanation: One function of the EIGRP hello packets is to ensure that EIGRP neighbors are still healthy and available. EIGRP hello packets are sent out in intervals according to the hello timer. The default EIGRP hello timer is 5 seconds on high-speed interfaces and 60 seconds on slow-speed interfaces (T1 or lower).

7. How can an EIGRP route be manipulated using offset lists?

  • Completely remove a specific set of component routes.
  • Reduce the total path metric to a more preferred value.
  • Add the total path metric to a specific set of routes.
  • Add delay to the path metric for a specific set of routes.

Explanation: Offset lists allow for the modification of route attributes based on the direction of the update, a specific prefix, or a combination of direction and prefix. An offset-list command is configured on a router to modify the metric value of a route. On the downstream neighbor, the path metric increases by the offset value specified in the offset list. The offset value is calculated from an additional delay value that was added to the existing delay in the EIGRP path attribute.

8. A network administrator is configuring the hello timer and the hold timer on an EIGRP router. What is a factor that the administrator needs to consider?

  • EIGRP hello intervals should be less than the EIGRP hold timers.
  • EIGRP hello intervals and hold timers must match between EIGRP neighbors to form an EIGRP adjacency.
  • EIGRP hold timers specify the minimum time that the router should wait to send the next hello.
  • EIGRP hello intervals specify the maximum time that the router should wait to receive the next hello.

Explanation: EIGRP hello packets are sent out in intervals according to the hello timer. EIGRP uses a second timer called the hold timer that defaults to three times the hello timer. The hold time decrements, and upon receipt of a hello packet, the hold time resets and restarts the countdown. If the hold time reaches 0, EIGRP declares the neighbor unreachable and notifies DUAL of a topology change. EIGRP neighbors can still form an adjacency if the timers do not match, but the hellos must be received before the hold time reaches zero.

9. A junior network engineer is learning about mechanisms to prevent routing loops on EIGRP. Which valuable piece of information can the network engineer learn about split horizon on an EIGRP network?

  • Split horizon is disabled by default on all interfaces.
  • Split horizon needs to be enabled on a Layer 2 Virtual Private Network.
  • Split horizon needs to be disabled on hub-and-spoke topologies.
  • Split horizon can only be disabled in global configuration mode.

Explanation: EIGRP enables split horizon on all interfaces by default. It can be disabled on a specific interface on EIGRP classic mode and named mode. Split horizon needs to be disabled on hub-and-spoke topologies such as Frame-Relay, Dynamic Multipoint Virtual Private Network, or Layer 2 Virtual Private Network.

10. When the distribute-list 1 in serial 0/0 command is used, which EIGRP routing updates would be permitted?

  • Routing updates that are received on the serial 0/0 interface and permitted by ACL 1.
  • Routing updates that are received on the serial 0/0 interface and permitted by prefix-list 1.
  • Routing updates that are received on the serial 0/0 interface and permitted by route-map 1.
  • Routing updates that are received on the serial 0/0 interface and permitted by offset-list 1.

Explanation: EIGRP supports filtering of routes as they are received or advertised from an interface. Filtering of routes can be matched against ACLs (named or numbered), IP prefix lists, route maps, and gateway IP addresses. It is accomplished with the distribute-list {acl-number | acl-name | prefix prefix-list-name | route-map route-map-name | gateway prefix-list-name} {in | out} [interface-id] command.

11. The show ip eigrp topology command output on a router displays a successor route and a feasible successor route to network 192.168.1.0/24. In order to improve network convergence, what does EIGRP do when the primary route to this network fails?

  • The router sends query packets to all EIGRP neighbors for a better route to network 192.168.1.0/24.
  • DUAL immediately recomputes the algorithm to calculate the next backup route.
  • Packets that are destined for network 192.168.1.0/24 are sent out the default gateway instead.
  • The backup route to network 192.168.1.0/24 is installed in the routing table.

Explanation: When EIGRP detects that it has lost a successor for a path, the feasible successor instantly becomes the successor route, providing a backup route. This route is installed in the routing table and the router sends out an update packet for that path because of the new EIGRP path metrics.

12. Which time interval is used by default to send EIGRP hello packets on high bandwidth interfaces?

  • 1 second
  • 5 seconds
  • 10 seconds
  • 20 seconds
  • 30 seconds

Explanation: One function of the EIGRP hello packets is to ensure that EIGRP neighbors are still healthy and available. EIGRP hello packets are sent out in intervals according to the hello timer. The default EIGRP hello timer is 5 seconds on high-speed interfaces and 60 seconds on slow-speed interfaces (T1 or lower).


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