EIGRP

Question 1

What is EIGRP’s benefits over RIP

Answer 1

Support for networks more than 255 hops away
Fast convergence time
Better metric calculations
Un-equal multi path costing

Question 2

What is the EIGRP successor route

Answer 2

the path with the lowest metric to the destination network.

Question 3

Successor

Answer 3

The router that is the next hop away on the successor route

Question 4

Feasible distance

Answer 4

The total distance from the router to the destination network.

Question 5

Reported distance

Answer 5

The distance from the successor router to the destination network.

Question 6

Feasibility condition

Answer 6

The feasibility condition is a calculation to determine if a route can become a feasible route.

Calculated by: if RD of the back up router < FD of the successor router then the condition is met.

Question 7

Feasible successor

Answer 7

A backup router that satisfies the feasibility condition.

Question 8

What does active and passive mean in the EIGRP topology table

Answer 8

Passive - the route is up and stable

Active - the router is recomputing the DUAL algorithm as there is a topology change.

Question 9

What IP number does EIGRP use to communicate

Answer 9

88

Question 10

What is the multicast address for EIGRP packets

Answer 10

224.0.0.10

Question 11

What are the different EIGRP packet types

Answer 11

Hello
request
update
query
reply

Question 12

What does the hello packet do

Answer 12

discover EIGRP neighbours and maintain relationships

Question 13

what does the request packet do

Answer 13

Used to get specific information from a neighbour

Question 14

what does the update packet do

Answer 14

Used to update neighbours when there is a topology change

Question 15

What does the query packet do

Answer 15

Used to search for a new route when successor route is down.

Question 16

What does the reply packet do

Answer 16

Sent in response to the query packet

Question 17

What is the default metric calculation

Answer 17

Total path delay in microseconds + the bandwidth of the slowest link (in the form of 10Gbps)

Question 18

What is the wide EIGRP metric used for

Answer 18

When using the standard metric with links higher than a Gb the delay is the same so the metric would be the same for 10Gbps and 50Gbps.

The wide metric allows you to input the exact delay.

K6 is introduced default value 0.

Question 18

Are wide metrics backwards compatible with normal metrics

Answer 18

yes

Question 18

What is the variance multiplier used for

Answer 18

UECMP, the variance is the amount of difference between the successor and feasible successor’s FD that will allow the feasible successor to be used in UECMP.

Question 18

Is UECMP on/off by default

Answer 18

Off variance is set to 1 by default to enable change to another whole number.

Question 18

What is the EIGRP hold timer and what is the default value

Answer 18

The hold timer is the amount of time the EIGRP router will wait if it has not received a hello packet before assuming route is dead.

default is 3x hello timer.

Question 18

What is the hello timer and what is the default timer

Answer 18

the interval between hello packets been sent to neighbours to confirm availability

default 5 seconds for interfaces ethernet and above E1 and 64k default timer is 60 seconds.

Question 18

What happens when a link goes down in EIGRP

Answer 18

Link goes line protocol down

The feasible successor route takes over as the successor route.

Update packet is sent to neighbours telling new path.

if there is no Feasible successor route then DUAL will recompute to destination network.

The router will send out a query packet to downstream routers with the delay set to infinity to inform them a link has gone active.

The neighbour will then either send a reply saying it has no route / If the query didn’t come from the successor then the router will reply with the route / the router will send queries to down stream routers.

Question 18

What does EIGRP route summarisation help

Answer 18

Improves network scaling.

Question 18

What command do you use to see the EIGRP topology table

Answer 18

show ip EIGRP topology