Networking Interview Questions

Basics
· Can you define protocol?
· Can you explain the concept of OSI layer?
· Can you explain the different layers in OSI model?
· Can you explain Application layer in OSI model?
· Can you explain Presentation layer in OSI model?
· Is it compulsory that compression, encryption and translation functions will be
used during communication?
· Can you explain Session layer in OSI model?
· What’s the concept of Simplex, Half Duplex and Full Duplex dialogs?
· What are the different types of dialogs in Session layer?
· Can you explain Transport layer in OSI model?
· Can you explain the concept of Congestion?
· Can you explain Network Layer?
· Can you explain Data link Layer?
· Can you explain the Physical layer?
· Can you explain what an IP address is?
· How to convert Decimal to Binary?
· How many IP addresses can come in IPV4?
· Can you explain the concept of Unicast IP address?
· Can you explain the concept of IP multicasting or multicast IP address?
· How many different types of subnet classful networks are present?
· What are the IP address ranges for public and private IP address?
· Why do we need class and how many different types of class exists?
· How are the IP addresses distributed between different classes?
· Can you explain what is classful IP addressing?
· Can you explain the concept of subnetting?
· What are the advantages of using subneting?
· If the host has the subnet ID why do we need a subnet mask?
· How is network address calculated from the subnet?
· What is the advantage of using classless addressing over classful addressing
scheme?
· Can you explain the concept of CIDR?
· Twist: - Can you explain superneting?
· Can you explain concept of custom subneting?
· What is the implication of increasing and decreasing subnet Bits?
· Why do we need to subtract two from number of hosts?
· Can you explain the concept of VLSM?
· Can you explain IP packet in detail?

Routers
· Can you explain the concept of DPU, Segments, Datagram, Frame and packet?
· What is IP datagram fragmentation and MTU?
· Can you explain in detail with example how data fragmentation works?
· Larger the IP datagram less the overhead, is it true or false?
· What is the minimum size of MTU bytes?
· Can you explain how optimal MTU size is calculated?
· How does the IP message finally reassemble?
· Can you explain the concept of Repeaters, Hubs, Bridges, Switches and Routers?
· On what layers do router, switches, bridges and hubs operate?
· Can you explain the concept of Layer 3 switches?
· What are CSU, DSU and TSU?
· What are the basic components of the router?
· Can you explain the WAN and LAN Interface in Routers?
· What are DB-15, DB-60 and RJ-45 in CISCO routers?
· Can you explain the concept of TTL?
· What is the concept of ICMP packets?
· Which operating system does CISCO have?
· Can you explain the concept of NAT?
· How is NAT implemented?
· Can you explain how actually NAT works?
· Why does collision occur in HUBS and repeaters?
· Can you explain the concept of Collision domain?
· What is the concept of routing tables?
· What is the use of route print?
· Can you explain how in detail how routing table looks like?
· How can you see route tables on the router?
· Can you explain the concept of static and dynamic routing?
· When to use Static routes and dynamic routes?
· How do you configure static routes on a router?
· Can you explain static default routes?
· What is the advantage of using Static default routes?
· Why do workstations have route tables?
· What is the concept of gateway of last resort?
· Can you explain the concept of routing protocol?
· What activities does routing protocol perform?
· What metrics are used by routing protocols to determine the best path?
· Can you explain what is interior and exterior routing protocols?
· Can you explain the concept of intradomain and interdomain routing protocols?
· Can you explain the concept of internet work and intranet work routing protocols?
· Which method does routing protocol use to determine shortest path?
· What is distance vector routing protocol?
· How do routers share information in Distance Vector routing?
· What is the main issue with routing by rumor?
· Can you explain the count-to- infinity problem in distance vector?
· How is metric or the cost calculated for Distance Vector routing protocol?
· What is the main issue with hop count metric issue?
· Can you explain how Link-State routing protocols work?
· Can you explain the concept of broad cast and multi-cast?
· Can you tell which protocols falls in Distance vector and which in Link-State?
· What’s the difference between distance vector and link-state protocol?
· Can you explain difference between Single path and Multipath?
· Can you explain route summarization?
· How are the series of IP combined in to one route path in route summarization?
· Can you explain RIP protocol?
· How is route table populated by RIP protocol?
· Can you explain convergence in networks?
· Can you explain RIP timers in detail?
· Can you explain routing loop issue in RIP protocol?
· How do we avoid routing loop issue in RIP?
· In RIP why do we have HOP count of 15?
· How do we disable auto-summarization in RIP?
· Can you explain IGRP?
· How does IGRP work?
· How many timers does IGRP have?
· How does IGRP calculate metric?
· Can multiple instance of IGRP run on one physical router?
· How is load balancing done in IGRP?
· What’s the command to configure IGRP?
· Can you explain EIGRP?
· What does neighbor terminology mean in EIGRP?
· What are different types of packets in EIGRP?
· How does EIGRP protocol update route information to its neighbors?
· What is the concept of successor in EIGRP?
· What is DUAL in EIGRP?
· Can you explain reported distance (RD), feasibility distance (FD) and Feasibility
condition (FC)?
· Can you explain the concept of successor and feasible successor?
· Can you explain passive and active route states?
· What is SIA or stuck in active?
· How do packets and timers in EIGRP work?
· What are the different tables used in EIGRP?
· Can you explain EIGRP metrics?
· Can you explain how EIGRP finds its successor and feasible successor?
· Can you explain Active and Passive route?
· Can you explain OSPF?
· How does OSPF populate route table?
· What are the different tables in OSPF?
· Can you explain different areas in OSPF?
· Can you explain different router types in OSPF?
· Can you explain Designated Router and Backup designated router?
· Can you explain different router states in OSPF?
· Can you explain different OSPF packet types?
· What are the different types of OSPF timers?
· How SPF algorithm does the route determination?
· Can you explain autonomous system?
· What are different types of dynamic protocols?
· Can you explain autonomous numbers in EGP?
· What is BGP?
· What is the concept of BGP speakers and Peers?
· What is EBGP and IBGP?
· What is RIB?
· Can you explain the concept of BGP confederations?
· What are BGP path attributes?
· What is the concept of NLRI?
· How are routing neighbors discovered in BGP?
· Can you explain how BGP does the decision process?
· What is the concept of redistribution?
· Can you explain the concept of one way redistribution and mutual distribution?
· How does metric translation takes place in redistributing routes?

Firewall
· Can you define what a FIREWALL is?
· What are the different types of firewalls?
· Can you explain packet filtering firewall?
· Can you explain circuit level gateway?
· Can you explain stateful inspection?
· What is Application Gateway?
· Is NAT a firewall?
· Are personal firewall actually firewalls?
· Can you explain the concept of demilitarized zone?
· What is the meaning of bastion host?
· What are the different types of firewall architectures?
· Can you explain dual home architecture?
· Can you explain screened host architecture?
· Can you explain screened subnet architecture?
· What is the use of perimeter area?
· What is IP spoofing and how can it be prevented?
· Which firewall have you worked with?

VPN
· Can you explain the difference between trusted and untrusted networks?
· Can you define in short what VPN is?
· What are the different types of VPN?
· What requirements should a VPN fulfill?
· How many ways are there to implement VPN architecture?
· What are the different ways authentication mechanism in VPN?
· Can you explain the basic of encryption in VPN?
· What’s the difference between Symmetric and Asymmetric cryptosystem?
· What are the different symmetric algorithms?
· What are the disadvantages of symmetric algorithms?
· What are the different asymmetric algorithms?
· Can you explain different components in PKI?
· What is a digital certificate?
· Can you explain tunneling?
· What is the concept of HA and FA in VPN tunneling?
· Can you explain VPN tunneled packet in detail?
· Can you explain voluntary and compulsory tunnels?
· Can you explain static and dynamic tunnels?
· Can you explain encapsulating, carrier and passenger protocol?
· On which layer does L2F, PPTP and L2TP operate?
· Can you explain PPP protocol?
· Can you explain PPP link process step by step?
· Can you explain PPP packet format?
· How does PPP use LCP for link control?
· Can you explain PPTP (Point-to-Point Tunneling Protocol)?
· What is GRE in PPTP?
· How does PPTP encapsulate data?
· Can you explain CHAP?
· Can you explain PAP?
· What does PPTP use for encryption and authentication?
· What is a L2F protocol?
· Can you explain the broader steps of how L2F establishes the tunnel?
· Can you explain how L2F data tunneling process works?
· How do we do encryption and authentication in L2F?
· Can you explain L2TP?
· Can you define LAC and LNS?
· How does L2TP process?
· How do we do encryption and authentication in L2TP?
· Can you explain what IPSec is?
· Can you give an overview of various components in IPSec?
· In IPSec what is SAD, SPD and SA’s?
· Can you explain in a generic manner the packet of IPSec?
· Can you describe the Authentication Header (AH) Protocol?
· What is ESP (Encapsulating Security Payload)?
· What is Transport and Tunnel mode?
· Can you explain IKE (Internet Key Exchange)?
· Can you explain IKE phases?
· Can you explain IKE modes?
· Can you explain transport and tunnel mode in detail with datagram packets?

Protocols and other questions
· What is NetBIOS protocol?
· Can you explain what the use of IGMP Protocol is?
· What are the different types of host in multicasting?
· Can you explain Ping and Tracert?
· How do you continuously ping an IP Address?
· How does Tracert actually work?
· What is the use of RTP and RTCP Protocol?
· Can you explain RTP in Detail?
· Can you explain RTP multiplexing in detail?
· Can you explain format of RTP and RTCP packets?
· Can you explain RSVP?
· Can you explain in detail how RSVP actually works?
· Can you explain RPC (Remote Procedure Calls)?
· Can you explain the RPC and Client server Architecture?
· Can you explain TCP IP Protocol?
· Can you explain the architecture of TCP IP Protocol?
· Can you explain TCP header in detail?
· Can you explain IP protocol?
· Can you explain the concept of CDMA?
· Can you explain the concept of DHCP?
· How does DHCP work?
· How can we configure DHCP?
· What is DNS?
· How do we control USB through a network?
· What is the difference between Windows 2000 and Windows 2003?
· What is a difference between a domain and workgroup?

Networking Interview Questions

What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point

What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.

Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.

What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.

What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.

What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between the PAD and the network, called X.29. Together, these three recommendations are often called "triple X"

What is frame relay, in which layer it comes?
Frame relay is a packet switching technology/protocol. It will operate in the data link layer.

What is terminal emulation, in which layer it comes?
Refers to making a computer respond like a particular type of terminal. Terminal emulation programs allow you to access a mainframe computer or bulletin board service with a personal computer.
Telnet is also called as terminal emulation. It belongs to application layer.

What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.



What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.

What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by Microsoft and IBM for the use on small subnets.

What is RAID?
Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren’t generally necessary for personal computers.
There are number of different RAID levels. The three most common are 0, 3, and 5:

What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.

What is Brouter?
Hybrid devices that combine the features of both bridges and routers. A Brouter understands how to route specific types of packets, such as TCP/IP packets. Any other packets it receives are simply forwarded to other network(s) connected to the device (this is the bridge function).

What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.

What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.

How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats

What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.




What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.

Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.

What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.

What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.

What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
• 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
• 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
• Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
• 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.

What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).

What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.

What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.

What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.


What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.

What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.

What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255

What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.

What are major types of networks and explain?
• Server-based network
• Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration

What are the important topologies for networks?
• BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.

• STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.

• RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.

What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.

What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

**Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.

What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).

What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router

Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.

What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.

What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.

What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.

What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.

What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.

What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.

Expand IDEA.
IDEA stands for International Data Encryption Algorithm.

What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.

What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.

What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.

What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.

What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.

What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).

What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.

What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.

What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.

What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.

What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.

What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.


What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.

What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.

What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.