Important Computer Networks Interview Questions
1. What are 10Base2, 10Base5 and 10BaseT Ethernet LANs
10Base2—An Ethernet term meaning a maximum transfer rate of 10 Megabits per
second that uses baseband signaling, with a contiguous cable segment length of
100 meters and a maximum of 2 segments.
10Base5—An Ethernet term meaning a maximum transfer rate of
10 Megabits per second that uses baseband signaling, with 5 continuous segments
not exceeding 100 meters per segment.
10BaseT—An Ethernet term meaning a maximum transfer rate of
10 Megabits per second that uses baseband signaling and twisted pair cabling.
2. What is the difference between an unspecified passive
open and a fully specified passive open, An unspecified passive open has the
server waiting for a connection request from a client.
A fully specified passive open has the server waiting for a connection from
a specific client.
3. Explain the function of Transmission Control Block
A TCB is a complex data structure that contains a considerable amount of
information about each connection.
4. What is a Management Information Base (MIB)
A Management Information Base is part of every SNMP-managed device. Each
SNMP agent has the MIB database that contains information about the device's
status, its performance, connections, and configuration. The MIB is queried by
5. What is anonymous FTP and why would you use it
Anonymous FTP enables users to connect to a host without using a valid login
and password. Usually, anonymous FTP uses a login called anonymous or guest,
with the password usually requesting the user's ID for tracking purposes only.
Anonymous FTP is used to enable a large number of users to access files on the
host without having to go to the trouble of setting up logins for them all.
Anonymous FTP systems usually have strict controls over the areas an anonymous
user can access.
6. What is a pseudo tty
A pseudo tty or false terminal enables external machines to connect through
Telnet or rlogin. Without a pseudo tty, no connection can take place.
7. What is REX What advantage does REX offer other similar
8. What does the Mount protocol do
The Mount protocol returns a file handle and the name of the file system in
which a requested file resides. The message is sent to the client from the
server after reception of a client's request.
9. What is External Data Representation
External Data Representation is a method of encoding data within an RPC
message, used to ensure that the data is not system-dependent.
10. What is the Network Time Protocol ?
11. BOOTP helps a diskless workstation boot. How does it
get a message to the network looking for its IP address and the location of its
Boot files BOOTP sends a UDP message with a subnetwork broadcast address and
waits for a reply from a server that gives it the IP address. The same message
might contain the name of the machine that has the boot files on it. If the boot
image location is not specified, the workstation sends another UDP message to
query the server.
12. What is a DNS resource record
A resource record is an entry in a name server's database. There are several
types of resource records used, including name-to-address resolution
information. Resource records are maintained as ASCII files.
13. What protocol is used by DNS name servers
DNS uses UDP for communication between servers. It is a better choice than
TCP because of the improved speed a connectionless protocol offers. Of course,
transmission reliability suffers with UDP.
14. What is the difference between interior and exterior
Interior gateways connect LANs of one organization, whereas exterior
gateways connect the organization to the outside world.
15. What is the HELLO protocol used for
The HELLO protocol uses time instead of distance to determine optimal
routing. It is an alternative to the Routing Information Protocol.
16. What are the advantages and disadvantages of the three
types of routing tables
The three types of routing tables are fixed, dynamic, and fixed central. The
fixed table must be manually modified every time there is a change. A dynamic
table changes its information based on network traffic, reducing the amount of
manual maintenance. A fixed central table lets a manager modify only one table,
which is then read by other devices. The fixed central table reduces the need to
update each machine's table, as with the fixed table. Usually a dynamic table
causes the fewest problems for a network administrator, although the table's
contents can change without the administrator being aware of the change.
17. What is a TCP connection table
18. 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.
19. What is RIP (Routing Information Protocol)
It is a simple protocol used to exchange information between the routers.
20. What is SLIP (Serial Line Interface Protocol)
It is a very simple protocol used for transmission of IP datagrams across a
21. 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
22. 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
23. 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.
24. 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.
25. 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.
26. What is Gateway-to-Gateway protocol
It is a protocol formerly used to exchange routing information between
Internet core routers.
27. 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).
28. 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.
29. 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
30. What is IGP (Interior Gateway Protocol)
It is any routing protocol used within an autonomous system.
31. What is Mail Gateway
It is a system that performs a protocol translation between different
electronic mail delivery protocols.
32. What is wide-mouth frog
Wide-mouth frog is the simplest known key distribution center (KDC)
33. 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.
34. 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.
35. What is region
When hierarchical routing is used, the routers are divided into what we 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.
36. What is multicast routing
Sending a message to a group is called multicasting, and its routing
algorithm is called multicast routing.
37. 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.
38. 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.
39. 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.
40. 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.
41. 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
42. Why should you care about the OSI Reference Model
It provides a framework for discussing network operations and design.
43. What is the difference between routable and non-
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
44. What is MAU
In token Ring , hub is called Multistation Access Unit (MAU).
45. 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.
46. 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 offered 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.
47. What is the range of addresses in the classes of
Class A 0.0.0.0 - 127.255.255.255
Class B 184.108.40.206 - 220.127.116.11
Class C 192.0.0.0 - 18.104.22.168
Class D 22.214.171.124 - 126.96.36.199
Class E 240.0.0.0 - 247.255.255.255
48. 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.
49. 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.
50. 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
51. 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.
52. What is Project 802
It is a project started by IEEE to set standards that 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.
53. 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.
54. 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.
55. 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.
56. What is attenuation
The degeneration of a signal over distance on a network cable is called
57. What is cladding
A layer of a glass surrounding the center fiber of glass inside a
58. What is RAID
A method for providing fault tolerance by using multiple hard disk drives.
59. 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.
60. 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.
61. 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.
62. What is terminal emulation, in which layer it comes
Telnet is also called as terminal emulation. It belongs to application
63. What is frame relay, in which layer it comes
Frame relay is a packet switching technology. It will operate in the data
64. 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 hte
PAD and the network, called X.29. Together, these three recommendations are
often called "triple X"
65. What is SAP
Series of interface points that allow other computers to communicate with
the other layers of network protocol stack.
66. What is subnet
A generic term for section of a large networks usually separated by a bridge
67. What is Brouter
Hybrid devices that combine the features of both bridges and routers.
68. 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
69. What are the different type of networking /
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
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
70. What is mesh network
A network in which there are multiple network links between computers to
provide multiple paths for data to travel.
71. 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.
72. 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
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.
73. What are major types of networks and explain
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
74. 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).
75. What is difference between baseband and broadband
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.
76. What are the possible ways of data exchange
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
77. 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.
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
78. What is point-to-point protocol
A communications protocol used to connect computers to remote networking
services including Internet service providers.
79. What are the two types of transmission technology
(i) Broadcast and (ii) point-to-point
80. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like
bit polarity, synchronization, clock etc. Communication means the meaning full
exchange of information between two communication media.