CCNA FAQ: EIGRP

CCNA FAQ: EIGRP

Question: Which of the following affect the calculation of EIGRP metrics when all possible default values are used? (Choose two answers.)
a. Bandwidth
b. Delay
c. Load
d. Reliability
e. MTU
f. Hop count

Answer: A and B

Question: How does EIGRP notice when a neighboring router fails?
a. The failing neighbor sends a message before failing.
b. The failing neighbor sends a “dying gasp” message.
c. The router notices a lack of routing updates for a period of time.
d. The router notices a lack of Hello messages for a period of time.

Answer: D

Question: Which of the following is true about the concept of EIGRP feasible distance?
a. A route’s feasible distance is the calculated metric of a feasible successor route.
b. A route’s feasible distance is the calculated metric of the successor route.
c. The feasible distance is the metric of a route from a neighboring router’s perspective.
d. The feasible distance is the EIGRP metric associated with each possible route to reach a subnet.

Answer: B. The Feasible Distance (FD) is, for all known routes to reach a subnet, the metric for the best of those routes. The best route is called the successor route, and it is added to the IP routing table.

Question: Which of the following is true about the concept of EIGRP reported distance?
a. A route’s reported distance is the calculated metric of a feasible successor route.
b. A route’s reported distance is the calculated metric of the successor route.
c. A route’s reported distance is the metric of a route from a neighboring router’s perspective.
d. The reported distance is the EIGRP metric associated with each possible route to reach a subnet.

Explanation: C. A route’s reported distance (RD) is the metric used by the neighbor that advertised the route. A router uses it to determine which routes meet the feasibility condition for whether the route can be a feasible successor route.

Question: Which of the following network commands, following the command router eigrp 1, tells this router to start using EIGRP on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1? (Choose two answers.)
a. network 10.0.0.0
b. network 10.1.1x.0
c. network 10.0.0.0 0.255.255.255
d. network 10.0.0.0 255.255.255.0

Explanation: A and C. The EIGRP network command supports a parameter of a classful network, enabling EIGRP on all interfaces in that classful network, or an address and wildcard mask. In the latter case, interface IP addresses that match the configured address, when applying ACL-like logic with the wildcard mask, match the command.

Question: Routers R1 and R2 attach to the same VLAN with IP addresses 10.0.0.1 and 10.0.0.2, respectively. R1 is configured with the commands router eigrp 99 and network 10.0.0.0. Which of the following commands might be part of a working EIGRP configuration on R2 that ensures that the two routers become neighbors and exchange routes? (Choose two answers.)
a. network 10
b. router eigrp 98
c. network 10.0.0.2 0.0.0.0
d. network 10.0.0.0

Explanation: C and D. The EIGRP network 10.0.0.2 0.0.0.0 command exactly matches the interface with address 10.0.0.2 because of the wildcard mask, enabling EIGRP on that interface. The EIGRP ASN value must match on both routers. The network 10 command is syntactically incorrect; the entire classful network must be configured.

Question: Examine the following excerpt from a router’s CLI:
P 10.1.1.0/24, 1 successors, FD is 2172416
via 10.1.6.3 (2172416/28160), Serial0/1
via 10.1.4.2 (2684416/2284156), Serial0/0
via 10.1.5.4 (2684416/2165432), Serial1/0
Which of the following identifies a next-hop IP address on a feasible successor route?
a. 10.1.6.3
b. 10.1.4.2
c. 10.1.5.4
d. It cannot be determined from this command output.

Explanation: C. The first number in parentheses is the computed metric for a route, and the second number is the reported distance (RD) for the route. The route through 10.1.6.3 is the successor route, so it is not a feasible successor route. For the other two routes, only
the third route’s RD is less than or equal to the feasible distance (the metric of the successor route).

Question: Which of the following must occur to configure MD5 authentication for EIGRP? (Choose two answers.)
a. Setting the MD5 authentication key via some interface subcommand
b. Configuring at least one key chain
c. Defining a valid lifetime for the key
d. Enabling EIGRP MD5 authentication on an interface

Explanation: B and D. The MD5 key must be configured. It is not configured with an interface subcommand, but rather as part of a key chain. The useful lifetime of a key may be configured, but it is not required.

Question: In the show ip route command, what code designation implies that a route was learned with EIGRP?
a. E
b. I
c. G
d. R
e. P
f. D

Answer: F

Question: There are three possible routes for a router to reach a destination network. The first route is from OSPF with a metric of 782. The second route is from RIPv2 with a metric of 4. The third is from EIGRP with a composite metric of 20514560. Which route will be installed by the router in its routing table?
A. RIPv2
B. EIGRP
C. OSPF
D. All three

Answer: B. Only the EIGRP routes will be placed in the routing table because it has the lowest administrative distance (AD), and that is always used before metrics.

Question: Which EIGRP information is held in RAM and maintained through the use of Hello and update packets? (Choose two.)
A. Neighbor table
B. STP table
C. Topology table
D. DUAL table

Answer: A, C. EIGRP maintains three tables in RAM: neighbor, topology, and routing. The neighbor and topology tables are built and maintained with the use of Hello and update packets.

Question: What will be the reported distance to a downstream neighbor router for the 10.10.30.0 network, with the neighbor adding the cost to this neighbor to find the true FD?
P 10.10.30.0/24, 1 successors, FD is 2297856
via 172.16.10.2 (2297856/128256), Serial0/0
A. Four hops
B. 2297856
C. 128256
D. EIGRP doesn’t use reported distances.

Answer: B. EIGRP does use reported distance, or advertised distance (AD), to tell neighbor routers the cost to get to a remote network. This router will send the FD to the neighbor router and the neighbor router will add the cost to get to this router plus the AD to fid the true FD.

Question: Where are EIGRP successor routes stored?
A. In the routing table only
B. In the neighbor table only
C. In the topology table only
D. In the routing table and the neighbor table
E. In the routing table and the topology table
F. In the topology table and the neighbor table

Answer: E. Successor routes are going to be in the routing table since they are the best path to a remote network. However, the topology table has a link to each and every network, so the best answer is topology table and routing table. Any secondary route to a remote network is considered a feasible successor, and those routes are found only in the topology table and used as backup routes in case of primary route failure.

Question: Which command will display all the EIGRP feasible successor routes known to a router?
A. show ip routes *
B. show ip eigrp summary
C. show ip eigrp topology
D. show ip eigrp adjacencies
E. show ip eigrp neighbors detail

Answer: C. Any secondary route to a remote network is considered a feasible successor, and those routes are found only in the topology table and used as backup routes in case of primary route failure. You can see the topology table with the show ip eigrp topology command.

Question: Which of the following commands are used when routing with EIGRP or EIGRPv6? (Choose three.)
A. network 10.0.0.0
B. eigrp router-id
C. variance
D. router eigrp
E. maximum-paths

Answer: B, C, E. EIGRP and EIGRPv6 routers can use the same RID, unlike OSPF, and this can be set with the eigrp router-id command. Also a variance can be set to provide unequal-cost load balancing, along with the maximum-paths command to set the amount of load-balanced paths.

Question: Serial0/0 goes down. How will EIGRP send packets to the 10.1.1.0 network?
Corp#show ip eigrp topology
[output cut] P 10.1.1.0/24, 2 successors, FD is 2681842
via 10.1.2.2 (2681842/2169856), Serial0/0
via 10.1.3.1 (2973467/2579243), Serial0/2
via 10.1.3.3 (2681842/2169856), Serial0/1
A. EIGRP will put the 10.1.1.0 network into active mode.
B. EIGRP will drop all packets destined for 10.1.1.0.
C. EIGRP will just keep sending packets out s0/1.
E. EIGRP will use s0/2 as the successor and keep routing to 10.1.1.0. 840 Chapter 19 u Enhanced IGRP

Answer: C. There were two successor routes, so by default, EIGRP was load-balancing out s0/0 and s0/1. When s0/0 goes down, EIGRP will just keep forwarding traffi out the second link s0/1. s0/0 will be removed from the routing table.

Question:What command do you use to enable EIGRPv6 on an interface?
A. router eigrp as
B. ip router eigrp as
C. router eigrpv6 as
D. ipv6 eigrp as

Answer: D. To enable EIGRPv6 on a router interface, use the command ipv6 eigrp as on individual interfaces that will be part of the EIGRPv6 process.

Question: What command was typed in to have these two paths to network 10.10.50.0 in the routing table?
D 10.10.50.0 [90/2297856] via 172.16.10.6, 00:00:20, Serial0/1
[90/6893568] via 172.16.10.2, 00:00:20, Serial0/0
A. maximum-paths 2
B. variance 2
C. variance 3
D. maximum-hops 2

Answer: C. The path to network 10.10.50.0 out serial0/0 is more than two times the current FD, so I used a variance 3 command to load-balance unequal-cost links three times the FD.

10. A route to network 10.10.10.0 goes down. How does EIGRP respond in the local routing table? (Choose two.)
A. It sends a poison reverse with a maximum hop of 16.
B. If there is a feasible successor, that is copied and placed into the routing table.
C. If a feasible successor is not found, a query will be sent to all neighbors asking for a path to network 10.10.10.0.
D. EIGRP will broadcast out all interfaces that the link to network 10.10.10.0 is down and that it is looking for a feasible successor.

Answer: B, C. First, a maximum hop count of 16 only is associated with RIP, and EIGRP never broadcasts, so we can eliminate A and D as options. Feasible successors are backup routes and stored in the topology table, so that is correct, and if no feasible successor is located, the EIGRP will flod its neighbors asking for a new path to network 10.10.10.0.

Question: You need the IP address of the devices with which the router has established an adjacency. Also, the retransmit interval and the queue counts for the adjacent routers need to be checked. What command will display the required information?
A. show ip eigrp adjacency
B. show ip eigrp topology
C. show ip eigrp interfaces
D. show ip eigrp neighbors

Answer: D. The show ip eigrp neighbors command allows you to check the IP addresses as well as the retransmit interval and queue counts for the neighbors that have established an adjacency.

Question: For some reason, you cannot establish an adjacency relationship on a common Ethernet link between two routers. Looking at the output shown here, what are the causes of the problem? (Choose two.)

A. EIGRP is running on RouterA and OSPF is running RouterB.
B. There is an ACL set on the routing protocol.
C. The AS numbers don’t match.
D. There is no default network accepted from incoming updates.
E. The K-values don’t match.
F. There is a passive interface set.

Answer: C, E. For EIGRP to form an adjacency with a neighbor, the AS numbers must match, and the metric K-values must match as well. Also, option F could cause the problem; we can see if it is causing a problem from the output given.

Question: Which are true regarding EIGRP successor routes? (Choose two.)
A. A successor route is used by EIGRP to forward traffic to a destination.
B. Successor routes are saved in the topology table to be used if the primary route fails.
C. Successor routes are flagged as “active” in the routing table.
D. A successor route may be backed up by a feasible successor route.
E. Successor routes are stored in the neighbor table following the discovery process.

Answer: A, D. Successor routes are the routes picked from the topology table as the best route to a remote network, so these are the routes that IP uses in the routing table to forward traffi to a remote destination. The topology table contains any route that is not as good as the successor route and is considered a feasible successor, or backup route. Remember that all routes are in the topology table, even successor routes.

Question: The remote RouterB router has a directly connected network of 10.255.255.64/27. Which two of the following EIGRP network statements could you use so this directly connected network will be advertised under the EIGRP process? (Choose two.)
A. network 10.255.255.64
B. network 10.255.255.64 0.0.0.31
C. network 10.255.255.64 0.0.0.0
D. network 10.255.255.64 0.0.0.15

Answer: A, B. Option A will work because the router will change the network statement to 10.0.0.0 since EIGRP uses classful addresses by default. Therefore, it isn’t technically a wrong answer, but please understand why it is correct for this question. The 10.255.255.64/27 subnet address can be confiured with wildcards just as we use with OSPF and ACLs. The /27 is a block of 32, so the wildcard in the fourth octet will be 31. The wildcard of 0.0.0.0 is wrong because this is a network address, not a host address, and the 0.0.0.15 is wrong because that is only a block of 16 and would only work if the mask was a /28.

Question: RouterA and RouterB are connected via their Serial 0/0 interfaces, but they have not formed an adjacency. Based on the following output, what could be the problem?
ccna-faq-eigrp2
ccna-faq-eigrp2.1
A. The metric K values don’t match.
B. The AS numbers don’t match.
C. There is a passive interface on RouterB.
D. There is an ACL set on RouterA.

Answer: C. To troubleshoot adjacencies, you need to check the AS numbers, the K-values, networks, passive interfaces, and ACLs.

Question: How many paths will EIGRPv6 load-balance by default?
A. 16
B. 32
C. 4
D. None

Answer: C. EIGRP and EIGRPv6 will load-balance across 4 equal cost-paths by default but can be confiured to load-balance across equal- and unequal-cost paths, up to 32 with IOS 15.0 code.

Question: What would your configurations be on RouterB based on the illustration? (Choose two.)
ccna-faq-eigrp3
A. (config)#router eigrp 10
B. (config)#ipv6 router eigrp 10
C. (config)#ipv6 router 2001:db8:3c4d:15::/64
D. (config-if)#ip eigrp 10
E. (config-if)#ipv6 eigrp 10
F. (config-if)#ipv6 router eigrp 10

Answer: B, E. EIGRP must be enabled with an AS number from global confiuration mode with the ipv6 router eigrp as command if you need to set the RID or other global parameters. Instead of confiuring EIGRP with the network command as with EIGRP, EIGRPv6 is confiured on a per-interface basis with the ipv6 eigrp as command.

Question: RouterA has a feasible successor not shown in the following output. Based on what
you can learn from the output, which one of the following will be the successor for
2001:db8:c34d:18::/64 if the current successor fails?
via FE80::201:C9FF:FED0:3301 (29110112/33316), Serial0/0/0
via FE80::209:7CFF:FE51:B401 (4470112/42216), Serial0/0/1
via FE80::209:7CFF:FE51:B401 (2170112/2816), Serial0/0/2
A. Serial0/0/0
B. Serial0/0/1
C. Serial0/0/2
D. There is no feasible successor.

Answer: C. There isn’t a lot to go on from with the output, but that might make this easier than if there were a whole page of output. Since s0/0/2 has lowest FD and AD, that would become the successor route. For a route to become a feasible successor, its reported distance must be lower than the feasible distance of the current successor route, so C is our best answer based on what we can see.

Question: You have an internetwork as shown in the following illustration with routers running IOS 12.4. However, the two networks are not sharing routing table route entries. What is the problem?
ccna-faq-eigrp4
ccna-faq-eigrp4.1
A. The variances don’t match between routers.
B. The metrics are not valid between neighbors.
C. There is a discontiguous network.
D. There is a passive interface on RouterB.
E. An ACL is set on the router.

Answer: C. The network in the diagram is considered a discontiguous network because you have one classful address subnetted and separated by another classful address. Only RIPv2, OSPF, and EIGRP can work with discontiguous networks, but RIPv2 and EIGRP won’t work by default (except for routers running the new 15.0 code). You must use the no auto-summary command under the routing protocol confiuration. There is a passive interface on RouterB, but this is not on an interface between RouterA and RouterB and won’t stop an adjacency

Question: Which should you look for when troubleshooting an adjacency? (Choose four.)
A. Verify the AS numbers.
B. Verify that you have the proper interfaces enabled for EIGRP.
C. Make sure there are no mismatched K values.
D. Check your passive interface settings.
E. Make sure your remote routers are not connected to the Internet.
F. If authentication is configured, make sure all routers use different passwords.

Answer: A, B, C, D. Here are the documented steps that Cisco says to check when you have an adjacency issue:
uu Interfaces between the devices are down.
uu The two routers have mismatching EIGRP autonomous system numbers.
uu Proper interfaces are not enabled for the EIGRP process.
uu An interface is configured as passive.
uu K values are mismatched.
uu EIGRP authentication is misconfigured.
CCNA Frequently Asked Questions CCNA Exam Questions with Explanation

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