Top 21 Network Troubleshooting Interview Questions You Must Prepare 08.Dec.2023

The DNS server can be a public server or the gateway address. If it is the gateway address, the DNS server address should be configured on the gateway. The DNS server should also be configured on the users TCP/IP adapter.

Physical Address: It’s called as MAC Address (48 bit)

Logical Address :  It’s Called as Ip Address   (IPv4 -32 bit &  IPv6 -128 bit)

Its used to connect same type of devices without using a switch/hub so that they can communicate.

Check the IP connectivity with the DHCP server from a system configured on the network. Test if the DHCP client and server service is started on the DHCP server and the client. Test if the DHCP server service is reachable using nmap.

IPCONFIG command is used to display the IP information assigned to a computer.

From the output we can find out the IP address, DNS IP address, gateway IP address assigned to that computer.

Public IP addresses:

A public IP address is any valid address, or number, that can be accessed over the Internet.  Internet standards groups, such as the Network Information Center (NIC) or the Internet Assigned Numbers Authority (IANA), are the organizations responsible for registering IP ranges and assigning them to organizations, such as Internet Service Providers (ISPs).

Private IP addresses:

A private IP address is any number or address assigned to a device on a private TCP/IP Local Area Network that is accessible only within the Local Area Network.  For a resource inside the Local Area Network to be accessible over the Internet, a device within the Local Area Network must be connected to the Internet with a public IP address, and the networking must be appropriately configured. 

The same Internet standards organizations have reserved the following three IP address ranges that will never be registered publicly:

First IP in block Last IP in block

Check the IP connectivity using ping. Check if port 23 is open on the router using nmap.

1.Straight Crimping  : Communication  bw the  Difference Devices 

   Ex.( System To Switch &  Switch to System or Modem)

 2.Cross Crimping : Communication  bw the  same Devices    

 Ex.( System To system &  Switch to switch)


  1. Orange white  orange Orange white  orange
  2. Green white    blue Green white    blue
  3. Blue white       green Blue white       green
  4. Brown white   Brown Brown white   Brown


  1. Orange white  orange Green white  Green
  2. Green white    blue Orange white    blue
  3. Blue white       green Blue white      Orange
  4. Brown white   Brown Brown white   Brown

Check the connectivity with the default gateway. Check if the DNS server is configured on the PC. Check if the appropriate port number is active using nmap on the DNS server.

ClassA : 1-126         N.H.H.H to126.255.255.254    - 16 million hosts on each of 127 networks.

ClassB  : 128 -191   N.N.H.H  1 to191.255.255.254 - 65,000 hosts on each of 16,000 networks.

ClassC: 192- 223   N.N.N.H to223.255.254.254 - 254 hosts on each of 2 million networks.

ClassD  : 224-239  - Reserved for multicast groups.

ClassE:  240-254   - Reserved for future use.

Ranges 127.x.x.x are reserved for loopback or local host

Range of 169.254.X.X is APIPA, stands for automatic private IP addressing

Hub (layer 1 Device):

  • Hubs, also known as repeaters, are network devices that can operate on layer-1 (I.e. the physical layer) to connect network devices for communication.
  • A common connection point for devices in a network (Physical Layer-Layer1). When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

Switch (layer 2 Device)::

  • Switches are network devices that operate on layer-2 of OSI model of communication.
  • Switches are also known as intelligent hubs.

 In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer(layer 3) of the OSI Reference Model .

Router (layer 3 Device): 

  • Routers are the network devices that operate at Layer-3 of OSI model of communication.
  • As layer-3 protocols have access to logical address (IP addresses) so routers have the capability to forward data across networks.
  • Sometimes routers are also known as layer-3 switches.

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP [Network Layer (Layer3)]

Subnet mask is used for identify the Network.


For a class A address,  a standard subnet mask is,

For a class B address,  a standard subnet mask is,

For a class C address,  a standard subnet mask is

Test basic connectivity with ping, Check with nmap if the ports are open (20 and 21). Check if a firewall is restricting traffic to the server.

When DHCP server is not available the Windows client computer assignes an automatic IP address to itself so that it can communicate with the network cmputers. This ip address is called APIPA. ITs in the range of to

APIPA stands for Automatic private IP addressing.

A default gateway is a routing device used to forward all traffic that is not addressed to a destination within the local network or local subnet. If you don’t have a default gateway, it is not possible to communicate with the network device/host of different networks.

Domain is created when we install Active Directory. It's a security boundary which is used to manage computers inside the boundary. Domain can be used to centrally administor computers and we can govern them using common policies called group policies. We can't do the same with workgroup.

Domain: Collecton of clients controlled by the server called Domain

Work Group : Colletion of Client network called Work Group

The theoretical length is 100 meters but after 80 meters you may see drop in speed due to loss of signal.

Ping the DNS server and check the response. Check with wireshark if DNS request and response packets are being sent and received.

PING: Packet Internet Gropper. It's a diagnostic utility, which diagnose connectivitybetween computers. It use ICMP: Internet Control Messaging protocol to send echorequests ( usually 4 packets) and receive echo replies (4 packets)