Networking Interview Questions

Networking Interview Questions

  • Abhijeet Singh
  • 23rd May, 2022

Networking Interview Questions

1) Explain What is a Network?

A network is a collection of computers, servers, mainframes, network devices, peripherals, or other devices connected to one another to allow the sharing of data. An excellent example of a network is the Internet, which connects millions of people all over the world.

2) What is point to point link?

A Point-to-point link-based system provides dedicated links between two devices. For example, a wired system that connects two computers together can be thought of a point-to-point link. This is in contrast to a broadcast system where one system connects multiple other devices. A good example of a point-to-point system is a telephone call where only two people are connected and communicating.

3) What is a node?

In telecommunications networks, a node is either a redistribution point or a communication endpoint. The definition of a node depends on the network and protocol layer referred to.

4) What are routers?

A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. Data sent through the internet, such as a web page or email, is in the form of data packets.

5) What is Network Topology?

Network topology is the arrangement of the elements of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial field busses and computer networks.

6) What is OSI Model?

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology.

7) What is Hub, Switch, and Router?

Hub: A hub, also called a network hub, is a common connection point for devices in a network. Hubs are devices commonly used to connect segments of a LAN.

Switch: A network switch is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer of the OSI model.

Router: A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet.

8) What is carrier sense multiple access collision detect (CSMA/CD)?

Carrier-sense multiple access with collision detection is a media access control method used most notably in early Ethernet technology for local area networking. It uses carrier-sensing to defer transmissions until no other stations are transmitting.

9) What is TCP and UDP?

TCP(Transmission Control Protocol), and UDP(User Datagram Protocol) are protocols for transmitting the data.

TCP: It is a transport layer connection-oriented protocol. It ensures reliable connection and secure data transmission between the connecting devices over the network. It first establishes a secure connection and then transmits the data. TCP transmits the data from one device to the other in the form of data blocks. It is quite slow in data transmission but has better functionalities like flow control, error control, and congestion control in the network. The TCP header is of 20-60 bytes, and thus include various information to enhance the reliability, but the overhead is increased. Due to its reliability, protocols like HTTP, FTP, etc. use TCP for proper data transmission over the network.

UDP: It is a transport layer connection-less protocol. It ensures the fast transmission of data between the connecting devices over the network. There is no overhead of establishing, maintaining, and terminating a connection in UDP. It is mainly used to transmit real-time data where we can not afford any transmission delays. UDP transmits the data from one device to the other in the form of continuous data streams. The UDP header is of fixed size, i.e., 8 bytes. It is unreliable in nature but faster in speed. Due to its transmission speed, protocols like DNS, DHCP, RIP, etc. use UDP for proper data transmission over the network.

10) Explain what is a firewall?

A firewall is a system designed to prevent unauthorized access to or from a private network. You can implement a firewall in either hardware or software form, or a combination of both. Firewalls prevent unauthorized Internet users from accessing private networks connected to the internet, especially intranets.

11) What is Wireshark?

Wireshark is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education.

12) List some benefits of VLANS?

Below are few benefits of using VLANs:

  • Simplified administration for the network manager.
  • Higher performance and reduced latency.
  • Improved security and easier fault management.
  • Improved quality of service?
  • Reduced size of the broadcast domains

13) What is an IP address?

An IP address is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two main functions: host or network interface identification and location addressing.

14) What is forward delay timer?

The forward delay timer is the time interval that is spent in the listening and learning state. Default Spanning Tree Protocol (STP) forward delay timer is 15 seconds. You can adjust the Spanning Tree Protocol (STP) forward delay timer to any value between 4 and 30 seconds.

15) What is tracert?

In computing, traceroute and tracert are computer network diagnostic commands for displaying the route and measuring transit delays of packets across an Internet Protocol network.


traceroute [-FIldnrv] [-f 1st_ttl] [-m max_ttl] [-p port#] [-q nqueries] [-s src_addr] [-t tos] [-w wait] [-g gateway] [-i iface] [-z pausemsecs] HOST [data size]

16) What is a spanning tree?

A spanning tree is a subset of Graph G, which has all the vertices covered with the minimum possible number of edges. Hence, a spanning tree does not have cycles and it cannot be disconnected.

17) What do you understand by BFD?

Bidirectional Forwarding Detection (BFD) is a network protocol that is used to detect faults between two forwarding engines connected by a link.BFD establishes a session between two endpoints over a particular link.

18) What is control Plane and data Plane?

Data plane: It refers to all the functions and processes that forward packets/frames from one interface to another.

Control plane: It refers to all the functions and processes that determine which path to use. Routing protocols, spanning tree, ldp, etc are examples.

19) What is OSPF neighborhood?

OSPF routers go through the seven states, called Down, Attempt/Init, Two ways, Exstart, Exchange, Loading and full while building adjacency with other OSPF speaking routers.

OSPF neighborhood is a relation of two routers that allows them to see and understand each other but nothing more. In particular, two OSPF neighbors do not exchange any routing information - the only packets they exchange is Hello packets.

20) What is DNS?

DNS stands for Domain Name System. Itis a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities.

21) What is MAC Address?

MAC (media access control) address is a unique identifier assigned to a network interface controller for use as a network address in communications within a network segment. This use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth.

22) What is H.323?

H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks. H.323 was originally promoted as a way to provide consistency in audio, video, and data packet transmissions in the event that a local area network (LAN) did not provide guaranteed service quality (QoS).

23) What is load balancing and Route reflector?

Load balancing: It is the process of distributing network traffic across multiple servers. This ensures no single server bears too much demand. By spreading the work evenly, load balancing improves application responsiveness. It also increases the availability of applications and websites for users.

Route reflector: A route reflector offers an alternative to the logical full-mesh requirement of internal border gateway protocol (IBGP). A route reflector acts as a focal point for IBGP sessions. The purpose of the RR is concentration.

24) List different types of IP Classes?

TCP/IP defines five classes of IP addresses: class A, B, C, D, and E. Each class has a range of valid IP addresses. The value of the first octet determines the class. IP addresses from the first three classes (A, B and C) can be used for host addresses. The other two classes are used for other purposes – class D for multicast and class E for experimental purposes.

25) What is static IP and dynamic IP?

Static IP: A static IP is an IP address that is fixed, meaning that it never changes. If you are connected to an Internet connection that is "always on", most likely you have a static IP address, although some of the "always-on" connections use dynamic IP addressing to make the installation process easier.

Dynamic IP: A dynamic Internet Protocol address (dynamic IP address) is a temporary IP address that is assigned to a computing device or node when it's connected to a network. A dynamic IP address is an automatically configured IP address assigned by a DHCP server to every new network node.

26) What is NAT?

NAT (Network address translation) is a method of remapping one IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device.

27) What is EPON/GPON technology?

EPON: EPON (Ethernet Passive Optical Network) is an Ethernet-based PON technology. It uses point-to-multipoint architecture, passive fiber transmission, and provides multiple services over Ethernet.

GPON: GPON is a point-to-multipoint access network. Its main characteristic is the use of passive splitters in the fiber distribution network, enabling one single feeding fiber from the provider to serve multiple homes and small businesses.

28) What is MPLS?

MPLS(Multiprotocol Label Switching) is a routing technique in telecommunications networks that directs data from one node to the next based on short path labels rather than long network addresses, thus avoiding complex lookups in a routing table and speeding traffic flows.

29) Explain TCP 3-way handshake?

THREE-WAY HANDSHAKE or a TCP 3-way handshake is a process that is used in a TCP/IP network to make a connection between the server and client. It is a three-step process that requires both the client and server to exchange synchronization and acknowledgment packets before the real data communication process starts.

30) What is a smartjack?

Smartjack is a smart and intelligent device placed right between the telephone company's demarcation and customer premises. It is a type of NID with capabilities beyond simple electrical connections, such as diagnostics.

31) What does 10Base-T mean?

10Base-T is the Ethernet wiring standard for 10 Mbps (megabits per second) for a maximum distance of approximately 100 meters per segment over unshielded twisted pair cables terminated with RJ-45 connectors.

32) What is WCCP?

WCCP (Web Cache Communication Protocol) is a Cisco-developed content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It has built-in load balancing, scaling, fault tolerance, and service-assurance mechanisms.

33) What is mesh topology?

Mesh topology is a type of networking where all nodes cooperate to distribute data amongst each other. This topology was originally developed 30+ years ago for military applications, but today, they are typically used for things like home automation, smart HVAC control, and smart buildings.

34) What is Peer-to-Peer Networking?

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes.

35) What is SLIP?

SLIP (Short for Serial Line Internet Protocol) is an Internet protocol that allows users to gain Internet access using a computer modem. Today, SLIP is not used as frequently as its successor, PPP (Point-to-Point Protocol), which provides enhanced error detection and automatic configuration.

36) What is metro ethernet?

A metropolitan-area Ethernet, Ethernet MAN, or metro Ethernet network is a metropolitan area network that is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or the Internet.

37) What are the BGP message types?

There are four BGP message types. They are

  • OPEN - Used to open a BGP communication session between peers. This is the first message sent by each side once the 3WHS is complete, and can be thought of as a HELLO. Only once each side has confirmed the OPEN message, the other message types can be exchanged.
  • UPDATE - Used to exchange routing information, such as announce new routes or withdraw previously announced routes.
  • KEEPALIVE - Notifies BGP peers that a device is active. Used to keep sessions (i.e long periods with no updates) from expiring.
  • NOTIFICATION - This message is a result of an error condition occurs. These message types are used to close an active session, and also inform the peer to the reason why.

38) What is Hybrid Network?

A hybrid network is any computer network that uses more than one type of connecting technology or topology. For example, a home network that uses both Wi-Fi and Ethernet cables to connect computers is a hybrid.

39) What is ICMP and Ping?

ICMP: ICMP (Internet Control Message Protocol) is an error-reporting protocol network devices like routers use to generate error messages to the source IP address when network problems prevent delivery of IP packets.

Ping: It is a computer network administration software utility used to test the reachability of a host on an Internet Protocol network. It is available for virtually all operating systems that have networking capability, including most embedded network administration software.

40) What is ethernet?

Ethernet is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3.

41) What is use of Default gateway?

A default gateway serves as an access point or IP router that a networked computer uses to send information to a computer in another network or the internet. The default simply means that this gateway is used by default unless an application specifies another gateway.

42) What are the LMHOSTS files?

The LMHOSTS file is a text file that maps Internet Protocol (IP) addresses to NetBIOS names of remote servers with which you wish to communicate over the TCP/IP protocol.

43) Explain what is port forwarding?

In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a communication request from one address and port number combination to another while the packets are traversing a network gateway, such as a router or firewall.

44) What is the convergence time?

Convergence time is a measure of how fast a group of routers reaches the state of convergence. It is one of the main design goals and an important performance indicator for routing protocols, which should implement a mechanism that allows all routers running the protocol to quickly and reliably converge.

45) What are T1 circuits?

A T1 Circuit is an Internet connection providing high-speed T1 bandwidth of 1.544Mbps delivered over fiber optic or copper phone lines. A T1 connection can also be configured by a T1 provider to carry voice services (Integrated T1) or for service higher than T1 bandwidth (Bonded T1).

46) What is peer to peer communication?

Peer-to-peer (P2P) computing or networking is a distributed application architecture that ... However, news servers communicate with one another as peers to propagate Usenet news articles over the entire group of network servers.

47) What is Sonet?

SONET is a communication protocol, developed by Bellcore – that is used to transmit a large amount of data over relatively large distances using optical fibre. With SONET, multiple digital data streams are transfered at the same time over the optical fibre.

48) What is Route flapping?

In a network where a link-state routing protocol is run, the flapping router will force all connected routers to frequently recalculate topology. In networks that use distance vector routing protocol, flapping routers trigger routing updates whenever there is a change of state, so in both cases, the constant route flapping prevents the network from converging.

Route flapping can be minimized or contained within a smaller portion of the network when route aggregation is used. An aggregate route will not be released when there is still at least one valid aggregated sub-network. This occurs because a flapping route that is part of the aggregated subnet will not affect the routers that receive the aggregate.

49) What is Ad value of Default Route?

Default route is generated via many ways (Static & Dynamic). In the case of Static Default Route, The AD value is 1. But in the case of dynamic, The AD value of Default Route can be the same as AD value of dynamic Routing Protocol.

50) What is Byte stuffing?

Byte stuffing is a mechanism to convert a message formed of a sequence of bytes that may contain reserved values such as frame delimiter, into another byte sequence that does not contain the reserved values.

51) Tell me something about proxy server?

A proxy server acts as a gateway between you and the internet. It's an intermediary server separating end users from the websites they browse. Proxy servers provide varying levels of functionality, security, and privacy depending on your use case, needs, or company policy.

52) What does DHCP stand for?

Dynamic Host Configuration Protocol (DHCP) is a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected.

53) What is EIGRP?

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers.

54) What is port no of ftp and telnet?

The default FTP port is TCP 21. FTP also uses TCP 20 in some conditions.

The Default port of Telnet is 23

55) What are the main characteristic of BGP?

The main characteristic of BGP is

  • BGP is an exterior gateway protocol (EGP) used in routing in the Internet. It is an interdomain routing protocol.
  • BGP is a path-vector routing protocol suited for strategic routing policies.
  • It uses TCP port 179 to establish connections with neighbors.
  • BGPv4 implements CIDR.
  • eBGP is used for external neighbors. It is used between different autonomous systems.
  • iBGP is used for internal neighbors. It is used within an AS.
  • BGP uses several attributes in the routing-decision algorithm.
  • It uses confederations and route reflectors to reduce BGP peering overhead.
  • The MED (metric) attribute is used between autonomous systems to influence inbound traffic.
  • Weight is used to influence the path of outbound traffic from a single router, configured locally.

56) What is MPLS?

MPLS (Multiprotocol Label Switching) is a routing technique in telecommunications networks that directs data from one node to the next based on short path labels rather than long network addresses, thus avoiding complex lookups in a routing table and speeding traffic flows.

57) What is ipconfig?

Ipconfig (sometimes written as IPCONFIG) is a command-line tool used to control the network connections on Windows NT/2000/XP machines. Ipconfig displays all current TCP/IP network configuration values and refreshes Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) settings.

58) What is DF bit in IP header?

DF means Don't Fragment. There are three-bit field follows and is used to control or identify fragments.

  • bit 0: Reserved; must be zero.
  • bit 1: Don't Fragment (DF)
  • bit 2: More Fragments (MF)

If the DF flag is set & fragmentation is required to route the packet, then the packet is dropped. This can be used when sending packets to a host that does not have sufficient resources to handle fragmentation.

For unfragmented packets, the MF flag is cleared. For fragmented packets, all fragments except the last have the MF flag set. The last fragment has a non-zero Fragment Offset field, differentiating it from an unfragmented packet.

59) What is IP fragmentation?

IP fragmentation is an Internet Protocol (IP) process that breaks packets into smaller pieces (fragments) so that the resulting pieces can pass through a link with a smaller maximum transmission unit (MTU) than the original packet size. The fragments are reassembled by the receiving host.

60) What are different types of networks?

A computer network is mainly of four types:

  • LAN(Local Area Network)
  • PAN(Personal Area Network)
  • MAN(Metropolitan Area Network)
  • WAN(Wide Area Network)

61) What is STP and RSTP?

STP: The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them.

RSTP: Rapid Spanning Tree Protocol (RSTP) is a network protocol that ensures a loop-free topology for Ethernet networks. Nowadays it is a popular solution to implement redundant networks in critical systems for Energy, Aerospace or Factory Automation. This protocol is incorporated into IEEE 802.1Q-2014.

62) What is asymmetric Routing?

Asymmetric routing is the situation where packets from A to B follow a different path than packets from B to A. Asymmetric routing is very common with BGP, and completely avoiding it is impossible. Asymmetric Routing Is an Efficient Way to Direct Network Packet Flow.

63) What is UDLD?

Unidirectional Link Detection (UDLD) is a data link (layer 2) protocol from Cisco Systems to monitor the physical configuration of the cables and detect unidirectional links. The goal of the UDLD protocol is to detect a broken bidirectional link.

64) What is HSRP?

HSRP (Hot Standby Router Protocol) is a routing protocol that allows host computers on the Internet to use multiple routers.It is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway.

65) What is multicast routing?

Multicast routing is a networking method for the efficient distribution of one-to-many traffic. A multicast source, such as a live video conference, sends traffic in one stream to a multicast group. The multicast group contains receivers such as computers, devices, and IP phones.

Multicast Routing using the following technologies:

  • Voice over IP (VOIP)
  • Video on demand (VOD)
  • Video conferencing
  • IP television (IPTV)

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