Network Connectivity between your computer and other computers

 To test network connectivity between your computer and other computers, you can use several tools and commands available in Debian/Ubuntu. Here are the most common methods:

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1. Ping – Basic Connectivity Test

ping <IP-address or hostname>

Example:

ping 192.168.1.1
ping google.com

Explanation:

• Sends ICMP echo requests to the target.
• If the target responds, it indicates basic connectivity.
• Useful for checking if a machine or server is reachable.

Options:

• -c <number> – Limit the number of packets.

  
  ping -c 4 google.com
  

• -i <seconds> – Set interval between pings.

  
  ping -i 2 192.168.1.1
  

• -t <ttl> – Set time to live (TTL).

  
  ping -t 64 8.8.8.8
  

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2. Traceroute – Path and Latency Test

traceroute <IP-address or hostname>

Example:

traceroute google.com

Explanation:

• Shows the path packets take to reach the target.
• Displays each hop along the way with latency details.

Install Traceroute (if not installed):

sudo apt install traceroute

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3. Netcat (nc) – Port Connectivity Test

nc -zv <IP-address or hostname> <port>

Example:

nc -zv 192.168.1.100 22

Explanation:

• Tests if a specific port is open on the target.
• -z – Scan without sending data.
• -v – Verbose output.

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4. Telnet – Port Testing

telnet <IP-address or hostname> <port>

Example:

telnet 192.168.1.1 80

Explanation:

• Checks if a port is open by initiating a connection.

Install Telnet (if not installed):

sudo apt install telnet

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5. Nmap – Comprehensive Network Scanning

nmap <IP-address or subnet>

Example:

nmap 192.168.1.0/24

Explanation:

• Scans for active hosts and open ports.
• Provides detailed information about available services.

Install Nmap (if not installed):

sudo apt install nmap

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6. Checking Routes – IP Route

ip route

Explanation:

• Displays the current routing table.
• Shows how packets will reach different networks.

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7. Checking DNS Resolution – Dig or Nslookup

dig <domain-name>
nslookup <domain-name>

Example:

dig google.com
nslookup google.com

Explanation:

• Tests if the system can resolve domain names to IP addresses.

Install Dig (if not installed):

sudo apt install dnsutils

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8. Curl or Wget – HTTP/HTTPS Connectivity Test

curl -I <URL>
wget --spider <URL>

Example:

curl -I https://www.google.com
wget --spider https://www.google.com

Explanation:

• Tests HTTP/HTTPS connectivity and checks if a webpage is accessible.

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9. ARP (Address Resolution Protocol) Test

arp -a

Explanation:

• Displays the ARP table showing IP-to-MAC mappings for hosts on the local network.

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10. Advanced – TCPDump for Network Traffic Analysis

sudo tcpdump -i eth0

Explanation:

• Captures and analyzes packets in real-time.

Install TCPDump (if not installed):

sudo apt install tcpdump

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Example Workflow for Testing Connectivity to Multiple Computers:

1. Ping multiple systems:

   
   ping -c 3 192.168.1.1
   ping -c 3 192.168.1.2
   ping -c 3 google.com
   

2. Traceroute to check path:

   
   traceroute 8.8.8.8
   

3. Scan the network to discover active hosts:

   
   nmap 192.168.1.0/24
   

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