EIGRP interview questions and answers part 1

EIGRP interview questions and answers part 1

1. Presented By - SIDDHARTH EIGRP Interview Questions & Answers Part -1

2. Question - What is EIGRP? Enhanced Interior Gateway Routing Protocol (EIGRP) is an enhanced distance vector routing protocol. It is also considered as a Hybrid Routing Protocol because it has characteristics of both Distance Vector and Link State Routing Protocols. EIGRP supports classless routing and VLSM, route summarization, incremental updates, load balancing and other features . Answer Networking Study Guide

3. Question - What is the maximum Hop-count for EIGRP? EIGRP  has a  maximum hop count  of 224. Answer Networking Study Guide

4. Question - What is the Multicast IP address used by EIGRP? EIGRP uses the multicast address 224.0.0.10 Answer Networking Study Guide

5. Question - What is Administrative value of EIGRP? EIGRP applies an Administrative Distance of 90 for routes originating within the local Autonomous System . EIGRP applies an Administrative Distance of 170 for external routes coming from outside the local Autonomous System Answer Networking Study Guide

6. Question - What are the Default Hello , Hold timers in EIGRP By default, on LAN and high-speed WAN interfaces , EIGRP Hellos are sent every 5 seconds . On slower WAN links (T1 speed or slower), EIGRP Hellos are sent every 60 seconds by default. By default, the Hold timer is three times the Hello timer . Thus , on highspeed links the timer is set to 15 seconds , and on slower WAN links the timer is set to 180 seconds . Answer Networking Study Guide

7. Question - What are the different K-values used in EIGRP? 1.Bandwidth  (K1=1) 2. Load (K2=0) 3. Delay (K3=1) 4. Reliability (K4=0) 5. Maximum Transmission Unit (K5=0) Note - By default, EIGRP only uses B andwidth   (K1)  and D elay   (K3)  to calculate metrics. Answer Networking Study Guide

8. Question - Which formula used in EIGRP to calculates metric? Metric = [( 10^7 / lowest-bandwidth) + cumulative-delay ] * 256 The lowest bandwidth is the lowest-bandwidth link in the route, using a unit of Kilobits per second . The cumulative-delay value used in the formula is the sum of all the delay values for all links in the route, with a unit of tens of microseconds. Answer Networking Study Guide

9. Question - What is the difference in metric calculation between EIGRP and IGRP? The EIGRP metric is obtained when you multiply the IGRP metric by 256. The IGRP uses only 24 bits in its update packet for the metric field, but EIGRP uses 32 bits in its update packet for the metric field. Answer Networking Study Guide

10. Question - Which algorithm EIGRP use for finding best path? EIGRP uses Diffusing Update Algorithm (DUAL) to determine the best path among all “feasible” paths. DUAL also helps ensure a loopfree routing environment. Answer Networking Study Guide

11. Question - What are the requirements for neighborship in EIGRP? 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. Answer Networking Study Guide

12. Question - Conditions for EIGRP neighbours Conditions for EIGRP neigbours are given below The routers must be able to send/receive IP packets to one another. Interfaces ’ primary IP addresses must be in same subnet. Must not be passive on the connected interface. Must use the same ASN (EIGRP) in the router configuration command. Must pass neighbor authentication (if configured ). K-values (used in metric calculation) must match Answer Networking Study Guide

13. Question - Explain the role of EIGRP Router ID? EIGRP automatically selects the highest IP address on any active loopback interface as the router ID. If there is no loopback interface then the highest IP address on any active interface is used. You can also overrule this by manually setting the router ID. Answer Networking Study Guide

14. Question - What is successor ? Successor is considered as the best path to distance from many paths. Answer Networking Study Guide

15. Question - What is the Feasible successor? A feasible successor is the second best path to reach a destination after successor. It acts as a backup for the successor. Answer Networking Study Guide

16. Question - What is the Feasible distance? Feasible distance is the distance (metric) to reach the destination network. The route with this metric will be in the routing table as it is the best route to reach a remote (destination) network. Answer Networking Study Guide

17. Question - What is Advertised Distance/Reported Distance? Advertised distance is the distance (metric) of a neighbor router to reach the destination network. This is the metric of a destination network as reported by a neighbor. Answer Networking Study Guide

18. Question - What is the Feasibility Condition in EIGRP? For any route to be a feasible successor it has to fulfil feasibility condition which is as follows:- The advertised distance of Feasible successor should be less than Feasible distance of Successor AD of feasible successor < FD of  successor Answer Networking Study Guide

19. Question - What authentication does EIGRP support? EIGRP supports Only MD5. Answer Networking Study Guide

20. Question - What are the different tables in EIGRP? Each EIGRP router uses three to store routing information: Neighbor table  – stores information about EIGRP neighbors. Before exchanging routes, routers need to establish a neighbor relationship. Information such as the IP address of the neighbor, the local interface on which the Hellos were received, the hold-down timer, and Smooth round-trip time are kept in this table. Topology table  – stores routing information learned from neighbor routing tables. This table stores every EIGRP route inside the autonomous system. The topology table also holds the metrics for each of the listed EIGRP routes, the feasible successor and the successors. Routing table  – stores only the best routes to reach a remote network. Answer Networking Study Guide

21. Question - What are different route types in EIGRP? There are three different types of routes in EIGRP : Internal Route —Routes that are originated within the Autonomous System (AS ). Summary Route —Routes that are summarized in the router (for example, internal paths that have been summarized ). External Route —Routes that are redistributed to EIGRP. Answer Networking Study Guide

22. Question - What are the different types of EIGRP Packets? 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 packets. Acknowledgement 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 does not have any 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. Answer Networking Study Guide

23. Question - Should I always use the EIGRP log-neighbor-changes command when I configure EIGRP? Yes , this command makes it easy to determine why an EIGRP neighbor was reset. This Reduces troubleshooting  time. Answer Networking Study Guide

24. Question - What are Graceful Shutdown and GoodBye message in EIGRP? When an EIGRP process is shut down, the router sends out “goodbye” messages to its neighbors. The neighbors can then immediately begin recalculating paths to all the destinations that went through that shutdown router without having to wait for the hold timer to expire. Answer Networking Study Guide

25. Question - Why no auto-summary command is used in EIGRP? By default, EIGRP behaves like a classful routing protocol which means it does not advertise the subnet mask information along with the routing information. No auto-summary command will ensure that EIGRP sends the subnet mask information along with the routing information. Answer Networking Study Guide

26. Question - Does EIGRP support aggregation and variable length subnet masks? Yes , EIGRP supports aggregation and variable length subnet masks ( vlsm ). Unlike open shortest path first ( ospf ), eigrp allows summarization and aggregation at any point in the network. Eigrp supports aggregation to any bit. This allows properly designed eigrp networks to scale exceptionally well without the use of areas. Eigrp also supports automatic summarization of network addresses at major network borders. Answer Networking Study Guide

27. Best of Luck !!!