CCNA and Networking Interview Questions

Hello friends. I hope this blog finds you all in good health and spirit. In continuation of my earlier blog which was interview questions for Windows Server 2008; this blog contains interview questions for CCNA and Networking. I have tried to provide to-the-point and precise answers. In this post I have not included any CLI questions. Have a look…

1. What is collision domain?
A Collision domain is any network segment in which collisions can happen. In other words, a collision domain consists of all the devices connected using a shared media where a collision can happen between any devices.
2. What is broadcast domain?
A Broadcast domain consists of all the devices that will receive any broadcast packet originating from any device within the network segment.
3. How many collision and broadcast domain is present in network device?
Device Collision Domain Broadcast Domain
Hub             Single                 Single
Switch         Multiple            Single
Router         Multiple            Multiple

4. On which OSI layer do hub, switch and router works?
Hub- Physical
Switch – Datalink
Router – Network
5. Explain CSMA/CD algorithm?
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a media access control method used in LAN to avoid and detect collision.
6. What is IOS?
IOS stands for Internetwork Operating System. IOS is used by Cisco routers and switches. It’s proprietary software first written in 1986 by William Yeager.
7. What is Autonomous System?
A group of networks under mutual administration that share the same routing methodology is called autonomous system.
8. What is routing?
Routing is a process of finding best path from source to destination. Routers maintain routing table for routing.
9. What is routing table?
Routing table is a database maintained by router in which it puts information regarding the networks associated with it either directly or indirectly. This routing table is used in order to decide which path should be followed in order to transfer a packet from source to destination.
10. Which command id used to see routing table?
Show ip route.
11. What is default route?
Default route is a special route that matches all destinations. Default routing is used only in stub networks. Stub are the networks that have only one output interface and everything going through these networks has to cross the single exit point.
12. What is administrative distance?
Administrative distance is the measure of trustworthiness of the source of the route. If a router learns about a destination from more than one routing protocol, administrative distance is compared and the preference is given to the routes with lower administrative distance.
13. Write down administrative distance for different protocols?
Connected 0
Static 1
eBGP 20
EIGRP (internal) 90
IGRP 100
OSPF 110
IS-IS 115
RIP 120
EIGRP (external) 170
iBGP 200
EIGRP summary route 5

14. What is metric?
Metric is a measure used by the routing protocol to calculate the best path to a given destination. If there are multiple paths to the same destination from a single routing protocol, then the multiple paths would have the same administrative distance and the best path is selected based on the metrics.
15. What are different memories used in routers?
Ram – It is working memory of router used to hold packet buffers, ARP cache, routing tables, and also the software and data structures that allow the router to function. Running configuration of router is stored in RAM, and most routers expand the IOS from flash into RAM upon boot.
Flash – Stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded. It is EEPROM (electronically erasable programmable read-only memory) created by Intel.
ROM – Used to start and maintain the router. Holds the POST and the Bootstrap program, as well as the mini-IOS.
NVRAM – Used to hold the router and switch startup configuration. NVRAM is not erased when the router or switch is reloaded. The configuration register is stored in NVRAM.
16. What is interior gateway protocol?
Interior gateway protocols are designed and intended to be used within an autonomous system. Eg – RIP, IGRP, OSPF, IS-IS and EIGRP. These protocols are further categorized into:
• Distance vector routing
• Link state routing
• Balanced hybrid

17. What is exterior gateway protocol?
Exterior gateway protocols are designed and intended to be used between different autonomous systems. Border gateway protocol (BGP) is mostly used EGP.
18. Explain distance vector routing algorithm?
The name distance vector is derived from the fact that routes are advertised as vectors of distance and direction, where distance is defined in terms of a metric and direction is defined in terms of the next-hop router. The protocols which work on this algorithm use hop count to determine best path. RIP and IGRP use this algorithm.
19. How many is maximum hop count for RIP protocol?
20. What is designated router in OSPF?
Designated router (DR) is responsible for propagation of all updates on its segment. We need DR because if all routers will start sending updates to each other the number of update packets will be huge. In case of the failure of DR there is going to be a Backup Designated Router elected to assume the role of DR.
21. What is Hello packet in OSPF?
OSPF works on neighbor relationship. For one router OSPF neighbor is another router that connects to the same data link with which the first router can and should exchange routing information using OSPF. Hello packet is used to discover neighbors.
22. What are LSA and LSDB in OSPF?
Link State Advertisement (LSA) is a special packet which each router exchanges with its neighbors. LSAs contain details such as: addresses/network masks configured on the links (interfaces running OSPF), the metric, the state of the link (which is its relation to the rest of the network), and list of neighbors connected to the link.
Each router stores the LSAs in its Link State Database (LSDB).
23. Explain OSPF area?
OSPF enabled routers have to share lot of information to each other. This consumes lot of resources as processing power and memory. To solve this problem network is break up in “area”. Routers in one area know less topology information about the subnets in the other area—and they do not know about the routers in the other area at all. So, configuring area reduces the size of LSDB and routing table for each router as they have entries only from their own area.
24. EIGRP is a __________________ protocol.
EIGRP is an advanced distance vector protocol or a balanced hybrid routing protocol.
25. How do EIGRP routers discover their neighbor?
EIGRP routers use EIGRP Hello messages, sent to multicast IP address, to discover their neighbors.
26. Which protocol is used to send EIGRP update packet?
Reliable Transport Protocol (RTP)
27. Explain EIGRP Successors and Feasible Successors.
EIGRP calculates the metric for each route to reach each subnet. For a particular subnet, the route with the best metric is called the successor and this route is entered in the routing table of router. The metric of the best route to reach a subnet is called Feasible Distance (FD). The routes whose metrics were larger than the FD for the route, EIGRP uses if the currently best route fails, without causing a routing loop. These alternative, immediately usable routes are called feasible successor routes, because they can feasibly be used when the successor route fails.
28. What is VLAN?
Switches support single broadcast domain by default. In order to create multiple broadcast domains we create virtual LAN (VLAN). One VLAN can’t communicate with another VLAN so it also enforce better security by keeping hosts that work with sensitive data on a separate VLAN.
29. What is trunking?
If there are multiple switches connected in a network, there is need to transfer VLAN information too in the frame as they may have common VLAN. This process of adding this information in the frame is called trunking.

30. Write down trunking protocols?
There are two trunking protocols – Inter-Switch Link (ISL) and IEEE 802.1Q. IEEE 802.1Q is the most popular trunking protocol.
31. What is VTP?
VLAN Trunking Protocol (VTP) is a Cisco protocol to facilitate automatic VLAN distribution between switches that use trunking connection.VTP is turned on by default but need few configurations to work.
32. What is VTP pruning?
By default, Cisco switches flood broadcasts (and unknown destination unicast) in each active VLAN via all trunks. However, in most networks, many VLANs exist on only a few switches and not on all switches. To solve the problem of this wasteful updates we configure VTP pruning. Pruning simply means that the appropriate switch trunk interfaces do not flood frames in that VLAN. VTP pruning, allows VTP to dynamically determine which switches do not need frames from certain VLANs, and then VTP prunes those VLANs from the appropriate trunks.
33. What is STP?
Spanning Tree Protocol (STP) is a protocol which prevents loops when multiple switches are connected in a network by placing each switch port in either a Forwarding State or a Blocking State.
34. Default priority for STP is ___________.
Default priority for STP is 32,768.
35. Write down default port cost for STP.
Ethernet Speed Cost
10 Mbps 100
100 Mbps 19
1 Gbps 4
10 Gbps 2

36. What is RSTP?
Rapid Spanning Tree Protocol (RSTP) is an improvement version of STP which converges faster than STP.
37. IEEE standard for STP and RSTP is ______________.
STP – IEEE 802.1d
RSTP – IEEE 802.1w.
38. What is circuit switching?
Circuit-switched is a type of network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. Ordinary voice phone service is an example of circuit-switching.
39. What is packet switching?
Packet-switched is a type of network in which data is divided into smaller units called packets and are routed through a shared network. Destination address is assigned on each packet. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Since in packet switching, path is not dedicated hence it uses network more efficiently than circuit switching. Most traffic over the Internet uses packet switching and the Internet is basically a connectionless network.
40. What is message switching?
Message switching is a network switching technique in which data is routed in its entirety from the source node to the destination node, one hop at a time. In message switching, the source and destination nodes are not directly connected. Instead, the intermediary nodes (mainly switches) are responsible for transferring the message from one node to the next. Before the advancements in packet switching, message switching acted as an efficient substitute for circuit switching but nowadays has been substituted by packet switching.
41. Explain x.25?
Originating in the 1970s, X.25 is a connection-oriented, packet-switching protocol, originally based on the use of ordinary analog telephone lines. Computers on an X.25 network carry on full-duplex communication, which begins when one computer contacts the other and the called computer responds by accepting the call. X.25 has no control over the actual path taken by the packets making up any particular transmission.
42. What is Frame relay?
Frame Relay is a standardized and fast wide area network technology. It puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. Frame relay is a packet-switched technology.
43. What is point to point protocol?
PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. It is a data link protocol and can provide connection authentication, encryption and compression.
44. What is ISDN?
Integrated Services for Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional ordinary telephone copper wire. ISDN in concept is the integration of both analog or voice data together with digital data over the same network. There are two levels of service provided by ISDN: the Basic Rate Interface (BRI), for the home and small enterprise, and the Primary Rate Interface (PRI), for larger users. Both services include a number of B-channels and D-channels. Each B-channel carries data, voice, and other services. Each D-channel carries control and signaling information.
45. What is ATM?
Asynchronous transfer mode (ATM) is a switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. ATM is designed to support both voice and data communications. ATM is normally utilized by Internet service providers on their private long-distance networks. ATM operates at the data link layer.
46. Explain FDDI.
Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network on fiber optic that can extend in range up to 200 km. The FDDI protocol is based on the token ring protocol. An FDDI network contains two token rings, one for possible backup in case the primary ring fails. The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps.

So, that’s all in this blog. I will keep updating the post for more questions. I will see you soon with some other technical stuff. Good bye and yes if going for any interview “Best of Luck”.


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