Computer Networks

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  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
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 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
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  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
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  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
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  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  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

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  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
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  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
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  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
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.

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  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.

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  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.
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. 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 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.