CCNA 3 Module 3

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S3 MODULE 3 - EIGRP v.3.0 1

CCNA 3 Module 3

3.1.1 1. When was EIGRP released by Cisco?
2. Is EIGRP compatible with IGRP?
3. What is the maximum hop count for
4. What is the maximum hop count for

5. What must both IGRP and EIGRP have
in common to communicate?
Same Autonomous System number
6. When using the “show ip route”
command, what letter is used for
EIGRP routes?
7. What routing tables does EIGRP

Neighbor table
Topology table
Routing table
8. Why is the neighbor table the most

The neighbor table is the most important table in
EIGRP. Each EIGRP router maintains a neighbor
table that lists adjacent routers. This table is
comparable to the adjacency database used by
OSPF. There is a neighbor table for each protocol
that EIGRP supports

9. What is DUAL?
Diffusing Update Algorithm – the distance vector
algorithm used by EIGRP

10. What is the topology table used for?

The topology table is made up of all the EIGRP
routing tables in the autonomous system. DUAL
takes the information supplied in the neighbor table
and the topology table and calculates the lowest
cost routes to each destination

11. What are the fields in the topology

Feasible distance, Route source, Reported
distance, Interface information, and Route status

12. What is a successor?

route selected as the primary route to use to reach
a destination. DUAL identifies this route from the
information contained in the neighbor and topology
tables and places it in the routing table
13. What is a feasible successor?

A backup route

14. How does the router view the feasible
DUAL identifies this route from the information
contained in the neighbor and topology tables and
places it in the routing table

15. What are external routes?

External routes originate outside the EIGRP AS.
Routes learned or redistributed from other routing
protocols, such as Routing Information Protocol
(RIP), OSPF, and IGRP, are external. Static routes
originating outside the EIGRP AS are external

S3 MODULE 3 - EIGRP v.3.0 2
16. What are the benefits of EIGRP?

Rapid convergence

Efficient use of bandwidth

Support for variable-length subnet mask
(VLSM) and classless interdomain routing (CIDR).
Unlike IGRP, EIGRP offers full support for
classless IP by exchanging subnet masks in
routing updates.

Multiple network-layer support

Independence from routed protocols. Protocol-
dependent modules (PDMs) protect EIGRP from
lengthy revision. Evolving routed protocols, such as
IP, may require a new protocol module but not
necessarily a reworking of EIGRP itself

17. Why do EIGRP routers converge more

EIGRP routers converge quickly because they rely
on DUAL. DUAL guarantees loop-free operation at
every instant throughout a route computation
allowing all routers involved in a topology change
to synchronize at the same time.
18. How does EIGRP make more efficient
use of bandwidth?

By sending partial, bounded updates and its
minimal consumption of bandwidth when the
network is stable. EIGRP routers make partial,
incremental updates rather than sending their
complete tables.

19. Which protocols does EIGRP support?
IP, IPX, and AppleTalk
20. How does EIGRP redistribute IPX, RIP,
and SAP information?
Through protocol-dependent modules (PDMs)
21. How does EIGRP take over for
AppleTalk RTMP?
EIGRP redistributes AppleTalk routing information
using event-driven updates. EIGRP also uses a
configurable composite metric to determine the
best route to an AppleTalk network

22. What is the rule for running EIGRP for

AppleTalk clients expect RTMP information from
local routers, so EIGRP for AppleTalk should be
run only on a clientless network, such as a wide-
area network (WAN) link.
23. How do EIGRP routers establish
relationships with their neighbors?

EIGRP routers establish adjacencies with neighbor
routers by using small hello packets. Hellos are
sent by default every five seconds. An EIGRP
router assumes that as long as it is receiving hello
packets from known neighbors, those neighbors
and their routes remain viable or passive. By
forming adjacencies, EIGRP routers do the
24. What does RTP (Reliable Transport
Protocol) do?
Transport-layer protocol that can guarantee
ordered delivery of EIGRP packets to all neighbors
25. Why is EIGRP protocol-independent?

It does not rely on TCP/IP to exchange routing
information the way that RIP, IGRP, and OSPF do.
To stay independent of IP, EIGRP uses RTP as its
own proprietary transport-layer protocol to
guarantee delivery of routing information.
26. What does RTP allow EIGRP to do?

With RTP, EIGRP can multicast and unicast to
different peers simultaneously, which allows for
maximum efficiency

S3 MODULE 3 - EIGRP v.3.0 3
27. What does FSM do for DUAL?
FSMs define a set of possible states that
something can go through, what events cause
those states, and what events result from those
states. Designers use FSMs to describe how a
device, computer program, or routing algorithm will
react to a set of input events.
3.1.5 28. What 5 packet types does EIGRP rely

Hello - Discover, veritfy and rediscover neighbor
Acknowledgment -
29. What IP do EIGRP routers send hellos
30. Where is neighbor information stored
Neighbor table

31. What is the Sequence Number field in
the neighbor table?
The neighbor table includes the Sequence Number
(Seq No) field to record the number of the last
received EIGRP packet that each neighbor sent
32. What is the default setting for the Hold
Three times the hello interval
33. What does EIGRP use
Acknowledgment Packets for?
To indicate receipt of any EIGRP packet during a
reliable exchange
34. Are Acknowledgment Packets multicast
or unicast?
35. What are Update Packets used for?
Update packets are also used when a router
detects a topology change
36. Are Update Packets multicast or
37. Who receives Update Packets?
All neighbors
39. What are Query Packets used for?
An EIGRP router uses query packets whenever it
needs specific information from one or all of its
41. What happens if EIGRP loses its
successor and cannot find a feasible
successor for a route?

DUAL places the route in the Active state. A query
is then multicasted to all neighbors in an attempt to
locate a successor to the destination network.
Neighbors must send replies that either provide
information on successors or indicate that no
information is available

3.2.1 42. What is the command to configure
Router(config)#router eigrp AS (autonomous
system number
43. What is the AS used for?
The autonomous system number is used to identify
all routers that belong within the internetwork. This
value must match all routers within the internetwork

44. What is the second step in configuring
the router for EIGRP? What is the
Indicating which networks belong to the EIGRP AS
Router(config-router)#network network-number

S3 MODULE 3 - EIGRP v.3.0 4
45. What also must be configured on the
serial links using EIGRP? What is the
It is important to configure the bandwidth setting on
the interface.
router(config-if)#bandwidth kilobits
46. What command enables logging of
neighbor adjacency changes?
router(config-if)#eigrp log-neighbor-changes
3.2.2 47. How is auto-summarization disabled?

router(config-router)#no auto-summary
48. What command is used to manually
configure a summary address?
router(config-if)#ip summary-address eigrp
autonomous-system-number ip-address mask

49. What is the default administrative
distance for EIGRP summary routes?
Can be configured for a value between 1 and
50. What is the normal administrative
distance of an EIGRP router?
51. Why must the auto-summarization be
turned off in the RTC configuration?
If auto-summarization was not turned off, RTD
would receive two routes, the manual summary
address, which is /16, and the automatic,
classful summary address, which is /8
3.2.3 52. Which commands help verify EIGRP

Show ip eigrp neighbors
Show ip eigrp interfaces
Show ip eigrp topology
Debug eigrp fsm
Debug eigrp packet
3.2.4 53. Which is the most important EIGRP
Neighbor table
54. What is the SRTT in the Neighbor
This is the average time that it takes to send and
receive packets from a neighbor. This timer is used
to determine the retransmit interval (RTO).
55. What is the Queue count in the
Neighbor Table?
This is the number of packets waiting in a queue to
be sent. If this value is constantly higher than zero,
there may be a congestion problem at the router.
3.2.5 56. Which memory contains EIGRP route
and topology information?
57. Which 2 routes does DUAL calculate?
Successor Route and Feasible Successor Route
3.2.6 58. What happens if both the successor
route and the feasible successor route
go down?
The route is flagged as Active
59. What happens once DUAL has
calculated a new successor route and
feasible successor route?
The route to the final destination will now pass from
an Active status to a Passive status. This means
that the route is now operational and reliable.
3.2.7 60. Which paths are considered the primary
or successor routes by DUAL?
Lowest-cost paths
61. Besides show and debug commands,
what other commands are used to test
Ping, extended ping, telnet, and traceroute
Covered in other sections of the Module or
in other Modules