EIGRP Terminology

Question 1

Successor route

Answer 1

The route with the lowest path metric to reach a destination.

The successor route for R1 to reach 10.4.4.0/24 on R4 is R1 → R3 → R4

Question 2

Successor

Answer 2

The best path to the destination route.

The successor for 10.4.4.0 /24 is R3.

Question 3

Feasible Distance (FD)

Answer 3

The distance advertised by a neighbor plus the cost
to get to that neighbor

Question 4

Reported Distance

Answer 4

The metric for a route advertised by a neighbor

Question 5

Feasibility condition

Answer 5

Feasible condition finds loop-free backup routes to the destination.

Question 6

Feasible Successor

Answer 6

A route that satisfies the feasibility condition and is maintained as a backup route.

The route R1 → R4 is the feasible successor because the RD 2816 is lower than the FD 3328 for the R1 → R3 → R4 path.

Question 7

What are the requirements for neighborship in EIGRP?

Answer 7

The following fields in a hello packet must match for routers to become neighbors:-
1. Autonomous System number.
2. K-values.
3. Authentication.
4. The primary address should be used.
5. If static neighborship then should be defined on both sides.

Question 8

What is the metric of the EIGRP protocol & its default values?

Answer 8

1. Bandwidth (K1=1)
2. Load (K2=0)
3. Delay (K3=1)
4. Reliability (K4=0)
5. Maximum Transmission Unit (K5=0)
   By default, EIGRP only uses Bandwidth (K1) and Delay (K3) to calculate metrics.

Question 9

What are the different packet types used by EIGRP?

Answer 9

The packet types used by EIGRP are:-

1. Hello - Neighborship is discovered and maintained by Hello Packets.
2. Acknowledgement - ACK packets are used to acknowledge the receipt of an update, query, and reply packet.
   Acknowledgment packets are Unicast.
3. Update - EIGRP uses Update messages to send routing information to neighbors. Update packets can be sent
   to a single neighbor using unicast or to a group of neighbors using multicast.
4. Query - Query packets are used when EIGRP router has lost path (Successor) to a certain network and has no backup paths (Feasible Successor). The router sends query packets to its neighbors asking them if they have information about this particular network. Query packets are multicast.
5. Reply - Reply packets are used in response to the query packets. Reply packets are unicast to the originator of
   the query.

Question 10

What is EIGRP Active State?

Answer 10

The condition when a route becomes unreachable and not all queries for it are answered; adjacencies with unresponsive neighbors are reset

Question 11

What is EIGRP Passive State?

Answer 11

A route is in a passive state for which the router has a successor route, and no failure has yet occurred. A stable EIGRP network will have all routes in a Passive state.