EIGRP

Question 1

What IP protocol number and multicast address is used by EIGRP

Answer 1

IP 88

Multicast address 224.0.0.10

Question 2

What are the 2 ADs given to EIGRP routes

Answer 2

90 for internal routes

170 for externally learned routes

Question 3

List the 5 packet types used to EIGRP for neighbor communication

Answer 3

Hellos
Updates
Acknowledgements 
Queries 
Reply’s

Question 4

What mechanism does EIGRP use to ensure reliable delivery of packets

Answer 4

RTP - reliable transport protocol

Question 5

What is the default hello and hold time for EIGRP

Answer 5

Hello - 5 seconds

Hold - 15 seconds

Question 6

What Information is carried in an EIGRP ‘Update’ packet

Answer 6

Updates contain route prefix and metric information. They are triggered when a new route is added, a cost change occurs or a route goes down.

They are only sent to neighbours that need them

Question 7

What Algorithm does EIGRP use to calculate cost to a prefix

Answer 7

DUAL - 5 k value metrics

Bandwidth, delay, reliability

Question 8

What is the path with the lowest cost called?

Answer 8

The feasible distance (FD)

The router with the lowest FD is the successor router.

Question 9

How does EIGRP ensure fast convergence when a router goes offline?

Answer 9

EIGRP elects a feasible successor and install this route in its routing table as a backup to the successor router.

Question 10

What does it mean when an EIGRP route is active?

Answer 10

The DUAL algorithm is actively computing a cost to the prefix

Question 11

What kinds of packets are sent when a route is active or in flux

Answer 11

Queries and replys

Question 12

What value does EIGRP set the FD of a route stuck in active

Answer 12

Infinity - a route of infinity will allow any new advertised distance to be installed as a successor.

Question 13

What does it mean when a EIGRP route is passive

Answer 13

The DUAL algorithm has arrived on a successor route to the prefix

Question 14

What is the default or “active” timer for an EiGRP query packet

Answer 14

3 minutes

Question 15

What happens when a route becomes stuck-in-active?

Answer 15

The router resets its adjacency with the neighbour router being queried

Question 16

What happens when EIGRP has 2 equal cost routes to a prefix?

Answer 16

EIGRP will use ECMP (equal cost multi pathing) and install both routes in the routing table

Question 17

What is the default number of successor routes EIGRP will install in its routing table?

Answer 17

4

This can be changed between 1-32

Question 18

How can you prevent EIGRP from using ECMP routes

Answer 18

By manipulating k values to modify cost (bandwidth/delay)

Question 19

What is CISCO express forwarding?

Answer 19

CEF is the default switching method used by routers to forward packets.

It is dependant on the FIB and Adjacency table

Question 20

What data does the forward information base hold?

Answer 20

The FIB contains the prefix of a route, the out going interface and next hop IP address.

Question 21

What does the adjacency table hold?

Answer 21

The adjacency table holds the protocol information (IP, IPv6), outgoing interface and precomputed layer 2 header.

Question 22

What is process switching?

Answer 22

Process switching involves referencing the routing table for each switched packet.

CPU intense!

Question 23

How do you enable unequal cost multi path in EIGRP

Answer 23

Using the variance metric multiplier

“Variance” command