Wednesday, December 9, 2009

Some basic networking 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
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
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
signaling and twisted pair cabling.
2. Explain 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
4. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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
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. Explain the difference between interior and exterior neighbor gateways
Interior gateways connect LANs of one organization, whereas exterior gateways connect the
organization to the outside world.
15. Explain 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
17. Explain a TCP connection table
18. Explain 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. Explain RIP (Routing Information Protocol)
It is a simple protocol used to exchange information between the routers.
20. Explain SLIP (Serial Line Interface Protocol)
It is a very simple protocol used for transmission of IP datagrams across a serial line.
21. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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. Explain Gateway-to-Gateway protocol
It is a protocol formerly used to exchange routing information between Internet core routers.
27. Explain 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. Explain 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. Explain 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. Explain IGP (Interior Gateway Protocol)
It is any routing protocol used within an autonomous system.
31. Explain Mail Gateway
It is a system that performs a protocol translation between different electronic mail delivery protocols.
32. Explain 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. Explain 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. Explain 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. Explain multicast routing
Sending a message to a group is called multicasting, and its routing algorithm is called multicast
37. Explain 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
38. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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. Explain 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
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. Explain the range of addresses in the classes of internet addresses
Class A -
Class B -
Class C -
Class D -
Class E -
48. Explain 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. Explain 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. Explain 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. Explain 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-architecturespecific,
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. Explain 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 noof-
bits represented by each signal shift.
55. Explain 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. Explain attenuation
The degeneration of a signal over distance on a network cable is called attenuation.
57. Explain cladding
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
58. Explain RAID
A method for providing fault tolerance by using multiple hard disk drives.
59. Explain 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. Explain redirector
Redirector is software that intercepts file or prints I/O requests and translates them into network
requests. This comes under presentation layer.
61. Explain 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. Explain terminal emulation, in which layer it comes
Telnet is also called as terminal emulation. It belongs to application layer.
63. Explain 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. Explain SAP
Series of interface points that allow other computers to communicate with the other layers of network
protocol stack.
66. Explain subnet
A generic term for section of a large networks usually separated by a bridge or router.
67. Explain 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
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.
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. Explain mesh network
A network in which there are multiple network links between computers to provide multiple paths for
data to travel.
71. Explain 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.
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
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.
RING topology:
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
regenerates it.
73. 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
Server-based networks provide centralized control of network resources and rely on server computers
to provide security and network administration
74. Explain 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. Explain 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
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
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 cellular telephony.
78. Explain 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 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.

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