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
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 SNMP.
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 utilities
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
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 operating system 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 neighbor gateways
Interior gateways connect LANs of one organization, whereas exterior gateways connect the organization to the outside
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
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 serial line.
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 beyond router.
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 routing decisions.
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
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
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 system.
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) authentication protocol.
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
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
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 network connection.
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
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 internet addresses
Class A 0.0.0.0 - 127.255.255.255
Class B 220.127.116.11 - 18.104.22.168
Class C 192.0.0.0 - 22.214.171.124
Class D 126.96.36.199 - 188.8.131.52
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
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 messages.
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
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
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
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
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 attenuation.
57. What is cladding
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
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
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 layer.
63. What is frame relay, in which layer it comes
Frame relay is a packet switching technology. It will operate in the data link layer.
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 or router.
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 formats.
69. What are the different type of networking / internetworking devices
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.
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.
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.
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.
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
In this each computer is directly connected to primary network cable in a single line.
Inexpensive, easy to install, simple to understand, easy to extend.
In this all computers are connected using a central hub.
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
In this all computers are connected in loop.
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
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 network administration
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 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.
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.
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.
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.
78. What is point-to-point protocol.
A communications protocol used to connect computers to remote networking services including Internet service
79. What are the two types of transmission technology available
(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.