CCNA Interview Questions and Answers for Experienced

41. Explain the loop avoidance mechanism in RIP.

The following methods are used to avoid Routing Loops in RIP:

• The maximum hop count mechanism can be used to block Routing Loops. Vector distance protocols use the TTL (Lifetime) value in the IP data header to avoid loops.
• Split horizontal is the setting of the route that stops the route from being advertised back to where it came from.
• Route Poisoning is another way to avoid loops. If the router finds that one of its connected routes has failed, the router will be toxic to the route by providing endless metrics to it.

For more details please refer to the  Routing Loop and How to Avoid Routing Loop article.

42. Why EIGRP is called hybrid protocol?

EIGRP does not transfer all data to the Routing table when changes are made, but will only transfer changes made since the Routing table was last updated. EIGRP does not send its routing table periodically, but will only send routing data in the event of a real change. This behavior is highly compliant with link-state routing regulations, so EIGRP is considered a hybrid protocol.

For more details please refer to the EIGRP fundamentals article.

43.  What is meant by active and passive states in EIGRP?

• Active State: Routes where a follower route fails and no follower routes are likely to move to a functional state forcing EIGRP to submit query packages and reconnect. 
• Passive State: The route is in a passive state where the route has a route to follow, and no failures have occurred so far.

For more details please refer to the EIGRP fundamentals article.

44. What does stuck-in-active mean?

EIGRP is a reliable protocol and for each question the route you send to its neighbors you must get a response within 3 minutes. If the router does not get an answer to ALL its pending questions it will set the stage for SIA (STUCK INACTIVE) and kill the nearest neighbor.

45.  What is the EIGRP Feasibility Condition?

The Feasibility condition states that the route will not be accepted if the Reported Range exceeds the best possible Route range. Or it means another way from a router’s point of view: the path to the network will not be accepted if my neighbor’s cost exceeds my cost. 

For more details please refer to the EIGRP Cost Calculation article.

46. Explain what will happen if the packet is not acknowledged?

If a packet is not acknowledged by the network, it means that the data was successfully delivered to its destination but no response was received from either end. As long as both ends are aware of each other and have been configured correctly, there should be no reason for the receiving node to do anything further with this packet. Data may still be flowing through this connection because acknowledgments take the time or because some intermediate nodes might be buffering packets before forwarding them on. However, if at any point in time you notice your traffic slowing down noticeably or becoming completely unavailable due to an excessive number of lost packets (especially during high-traffic times), then it’s likely that something has gone wrong and you’ll need to investigate what caused it.

For more details please refer to the Stop and Wait for protocol, and its problems, and solutions article.

47. Explain Null Zero in EIGRP?

It is a visual interface used to ensure that routes enter the RIB, the tracks must have the next-hop to get into the RIB. If a packet arrives on a device with a route to Null 0 and is not elsewhere, it will dispose of it as the ACL would. Think of it as a visible interaction when the packets die well.

For more details please refer to the article EIGRP fundamentals 

48.  What is the EIGRP stub routing feature?

The EIGRP stub routing feature allows the network administrator to prevent queries from being sent to a remote device. In addition to a simple hub and spoke network, where the remote device is connected to a single distribution device, the remote device can have a dual home on two or more distribution devices.

49. Difference between LSA & LSU in OSPF?

Link State Update (LSU) packs are OSPF Type 4. packs. Each LSA contains route, metrics, and topology information to define part of the OSPF network. The local router advertises the LSA inside the LSU package to its neighbors.

50.  What is Route Redistribution in computer networks?

The use of a routing protocol to broadcast routes that are known by some other means, such as by another routing protocol, static routes, or directly connected routes, is called redistribution. While operating a single routing protocol throughout your whole IP internetwork is desirable, multi-protocol routing is common for a number of reasons, such as enterprise unions, multiple departments controlled by multiple network administrators, and multi-vendor environments. Running other routing protocols is usually part of a network design. In any case, having a multiple protocol environment makes redistribution a need.

CCNA (Cisco Certified Network Associate) is a certification that proves your ability to understand, use, and manage Cisco networks. The CCNA certification provides you with the skills necessary for optimizing and administering Cisco networking resources in an organization. With this credential, you can move on to higher-level certifications such as the MCSA or MCDBA. Obtaining CCNA certification improves your knowledge base and enhances your job prospects.

In this article, we have filtered the top 50 CCNA interview questions with their answers that are most frequently asked for Freshers and Experienced candidates.

Let’s begin with CCNA Interview Questions for Freshers in the increasing order of difficulty.