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Chapter 17: Enhanced IGRP
1. 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.
2. 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.
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3. 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 find the true FD.
4. 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.
5. 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.
6. 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.
7. 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 traffic out the second link s0/1. s0/0 will be removed from
the routing table.
8. 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.
9. 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. 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 flood its neighbors asking for a new
path to network 10.10.10.0.
11. 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.
12. 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.
13. 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 traffic 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.
14. 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 configured 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.
15. C. To troubleshoot adjacencies, you need to check the AS numbers, the K values, networks, passive
interfaces, and ACLs.
16. C. EIGRP and EIGRPv6 will load-balance across 4 equal-cost paths by default but can be configured to load-
balance across equal- and unequal-cost paths, up to 32 with IOS 15.0 code.
17. B, E. EIGRP must be enabled with an AS number from global configuration mode with the
ipv6 router
eigrp as
command if you need to set the RID or other global parameters. Instead of configuring EIGRP
with the network command as with EIGRP, EIGRPv6 is configured on a per-interface basis with the
ipv6
eigrp as
command.
18. 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 the 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.
19. 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 configuration.
There is a passive interface on RouterB, but this is not on an interface between RouterA and RouterB and
won’t stop an adjacency.
20. A, B, C, D. Here are the documented issues that Cisco says to check when you have an adjacency issue:
1. Interfaces between the devices are down.
2. The two routers have mismatching EIGRP autonomous system numbers.
3. Proper interfaces are not enabled for the EIGRP process.
4. An interface is configured as passive.
5. K values are mismatched.
6. EIGRP authentication is misconfigured.
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