CCNA Job Interview Questions & Answers

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Q1. What are three types of LAN traffic?

Ans. Unicasts – intended for one host.
Broadcasts – intended for everyone.
Multicasts – intended for a only a subset or group within an entire network.

Q2. What are unicast frames?

Ans. Unicast frames are the most common type of network traffic. A unicast frame is a frame intended for only one host. The only station that processes this frame is one station that has its own MAC address in the destination portion of packet.

Q3. How do you enable IGRP on a Cisco router?

Ans. The way you enable IGRP on a Cisco router is similar to the way you enable RIP, except you specify IGRP as the protocol and add an autonomous system number. For example:
RouterA(config)# router igrp 10 (10 is the AS number)
RouterA(config-router)# network 192.168.0.0
RouterA(config-router)# network 192.168.1.0
RouterA(config-router)# network 192.168.2.0

Q4. What is Interior Gateway Routing Protocol (IGRP)?

Ans. IGRP is a Cisco proprietary distance vector routing protocol. IGRP has a default hop count of 100 hops, with a maximum hop count of 255. IGRP uses bandwidth and line delay as its default metric, but it can also use reliability, load, and MTU.

Q5. What is the destination address of broadcast frames?

Ans. The destination address of broadcast frames (Layer 2 broadcast addresses) is FF-FF-FF-FF-FF-FF, or all 1s in binary.

Q6. What is the difference between bridges and switches?

Ans. Bridges and switches function the same way; the only difference is in how they are implemented. Bridges are implemented by software and usually have a couple of network ports. Switches are implemented in hardware by ASIC chips and have many ports.

Q7. What is the Spanning-Tree Protocol (STP)?

Ans. STP is a loop-prevention bridge-to-bridge protocol. Its main purpose is to dynamically maintain a loop-free network. It does this by sending out Bridge Protocol Data Units (BPDUs), discovering any loops in the topology, and blocking one or more redundant links.

Q8. In spanning tree, what is a Bridge ID (BID)?

Ans. A BID is an 8-byte field that is composed of the bridge’s 6-byte MAC address and a 2-byte bridge priority.

Q9. What is the default bridge priority in a Bridge ID for all Cisco switches?

32,768

Q10. In.In spanning tree, what is path cost?

Ans. Path cost is a calculation to determine the link’s bandwidth. It is a value assigned to each port that is based on the port’s speed.

Q11. How do bridges pass spanning tree information between themselves?

Ans. Bridges pass STP information using special frame called Bridge Protocol Data Units (BPDUs).

Q12. How often do bridges send BPDUs out active ports?

The default time that bridges send BPDUs out active ports is 2 seconds.
Note: All ports on a switch listen for BPDUs in case there is a topology change.

Q13. What is the STP blocking state?

Ans. When a switch starts, all ports are in the blocking state. This is to prevent any loops in the network. If there is a better path to the root bridge, the port remains in the blocked state. Ports in the blocked state cannot send or receive traffic, but they can receive BPDUs.



Q14. What is the STP listening state?

Ans. Ports transition from a blocked state to a listening state. In this state, no user data is passed. The port only listens for BPDUs. After listening for 15 seconds (if the bridge does not find a better path), the port moves to the next state, the learning state.

Q15. What is the STP learning state?

Ans. In the STP learning state, no user data is being passed. The port quietly builds its bridging table. The default time in the learning state is 15 seconds.

Q16. What is the STP forwarding state?

Ans. After the default time in the learning state is up, the port moves to the forwarding state. In the forwarding state, the port sends and receives data.

Q17. What is STP forward delay?

Ans. The forward delay is the time it takes for a port to move from the listening state to the learning state or from the learning state to the forwarding state. The default time is 30 seconds.

Q18. What is the hello time in STP timers?

Ans. The hello time is the time interval between the sending of BPDUs. The default time is 2 seconds.

Q19. What is the Max Age timer?

Ans.The Max Age timer is how long a bridge stores a BPDU before discarding it. The default time is 20 seconds (ten missed hello intervals).

Q20. What is the default time a port takes to transition from the blocking state to the forwarding state?

Ans.The default time a port takes to transition from the blocking state to the forwarding state is 50 seconds: 20 seconds for Max Age, 15 seconds for listening, and 15 seconds for learning.

Q21. What does STP do when it detects a topology change in the network due to a bridge or link failure?

Ans. If spanning tree detects a change in the network due to a bridge or link failure, at least one bridge interface changes from the blocking state to the forwarding state, or vice versa.

Q22. Describe the central office (CO)?

Ans. The CO is the telco switching facility that connects the customer to the provider’s switching network. The CO is sometimes referred to as a point of presence. It is the point where the local loop gains access to the service provider’s access lines.

Q23. What is the toll network?

Ans. All the telco switches, COs, and trunk lines inside the WAN provider’s network are the toll network.

Q24. What are synchronous links?

Ans. Synchronous links have identical frequencies and contain individual characters encapsulated in control bits, called start/stop bits that designate the beginning and end of each character. Synchronous links try to use the same speed as the other end of a serial link.

Q25. What are Asynchronous links?

Ans. Asynchronous links send digital signals without timing. Asynchronous links agree on the same speed, but there is no check or adjustment of the rates if they are slightly different. Only 1 byte per transfer is sent.

Q26. What are the three layers of the Cisco Hierarchical Model?

Ans. The three layers of the Cisco Hierarchical Model are: 1
the access layer
The distribution layer
The core layer

Q27. How do you enable IGRP on a Cisco router?

Ans. The way you enable IGRP on a Cisco router is similar to the way you enable RIP, except you specify IGRP as the protocol and add an autonomous system number. For example:
RouterA(config)# router igrp 10 (10 is the AS number)
RouterA(config-router)# network 192.168.0.0
RouterA(config-router)# network 192.168.1.0
RouterA(config-router)# network 192.168.2.0

Q28. What is flow control, and what are the three methods of implementing it?

Ans. Flow control is the method of controlling the rate at which a computer sends data, thus preventing network congestion. The three methods of implementing flow control are
Buffering
Congestion avoidance
Windowing
Almost certain to be on the exam.




Q29. The IEEE defines what two sublayers of the data link layer?

Ans.The two sublayers of the data link layer are
The Logical Link Control (LLC) sublayer
The Media Access Control (MAC) sublayer
These two sublayers provide physical media independence.

Q30. What are some network devices that operate at the data link layer?

Ans. Bridges and switches are network devices that operate at the data link layer. Both devices filter traffic by MAC addresses.

Q31. The Ethernet and IEEE 802.3 standards define what three physical wiring standards that operate at 10 Mbps?

Ans. These physical wiring standards operate at 10 Mbps:
10Base2
10Base5
10BaseT

Q32. What are broadcast domains?

Ans. A broadcast domain defines a group of devices that receive each others’ broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower your network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.

Q33. What is the difference between a routing protocol and a routed protocol?

Ans. Routing protocols determine how to route traffic to the best location of a routed protocol. Examples of routing protocols are RIP, EIGRP, OSFP, and BGP. Examples of routed protocols are IP and IPX.

Q34. What 3 devices are used to segment a LAN?

Ans. Router
Switch
Bridge

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