Linux, BASH commands, Networking, CCNP/CCIE - GUIDE ((--- NETWORK BASH COMMANDS ---

1. Check Network Interfaces

• Command: ip a or ifconfig
• Purpose: Display all network interfaces and their IP addresses.

Manipulate IP Addresses with ip

• Purpose: Advanced IP address and routing configuration.
• Add an IP Address:

  sudo ip addr add 192.168.1.100/24 dev eth0

• Add a Route:

  sudo ip route add 192.168.2.0/24 via 192.168.1.1

• Delete a Route:

  sudo ip route del 192.168.2.0/24

Set a Static IP Address

• Command: Edit /etc/network/interfaces: or use nmcli
• Purpose: Configure a static IP address.
• Example: Edit /etc/network/interfaces:

  sudo nano /etc/network/interfaces

  Add:

  auto eth0
  iface eth0 inet static
      address 192.168.1.100
      netmask 255.255.255.0
      gateway 192.168.1.1
  

---

2. Test Connectivity (Ping)

• Command**: ping <URL>
• Purpose**: Test connectivity to a remote host. - Example: To stop after 5 packets:

  ping -c 5 google.com #-c = count 

---

3. Trace Route

• Command: traceroute <URL> or tracepath <URL>
• Purpose: Trace the path packets take to reach a destination.

---

4. Check DNS Resolution

• Command: nslookup <URL> or dig <URL>
• Purpose: Query DNS records for a domain.

Flush DNS Cache

• Command: sudo systemd-resolve --flush-caches
• Purpose: Clear the local DNS cache.

Analyze DNS Traffic with dnstop

• Purpose: Monitor DNS queries in real-time.
• Command:

  sudo dnstop eth0

---

5. Check Open Ports

• Command: netstat -tuln or ss -tuln
• Purpose: Display open ports and listening services.

Monitor Network Connections with ss

• Purpose: Advanced socket statistics.
• Command:

  ss -tulnp

• Advanced Options:
  • Show established connections:

    ss -tun state established

  • Filter by port:

    ss -tun sport = :80

---

6. Scan Network for Hosts

• Command: nmap
• Purpose: Scan a network for active hosts and open ports.
• Example:

  nmap -sP 192.168.1.0/24 #-Sp (scan port) <ipv4/netmask> 
  

  Scan a specific IP for open ports:

  nmap 192.168.1.1

Advanced nmap Scanning

• Purpose: Perform detailed network discovery and vulnerability scanning.
• Command:

  sudo nmap -A -T4 <target>

  • -A: Enable OS detection, version detection, script scanning, and traceroute.
  • -T4: Aggressive timing template.
• Advanced Examples:
  • Scan for UDP services:

    sudo nmap -sU <target>

  • Scan with a specific NSE script:

    sudo nmap --script=http-title <target>

---

7. Check Routing Table

• Command: ip route or route -n
• Purpose: Display the routing table.

---

8. Capture Network Traffic

• Command: tcpdump -i eth0
• Purpose: Capture and analyze network packets.
• Example: `` ` Capture only HTTP traffic:

  tcpdump -i eth0 port 80 

Capture and Analyze Packets with tcpdump

• Advanced Usage: Save packets to a file and analyze them later.
• Command:

  sudo tcpdump -i eth0 -w capture.pcap

  • -i eth0: Capture on interface eth0.
  • -w capture.pcap: Save packets to capture.pcap.
• Analyze the file:

  tcpdump -r capture.pcap

---

9. Simulate Network Issues with tc

• Purpose: Simulate network latency, packet loss, and bandwidth limits.
• Add Latency:

  sudo tc qdisc add dev eth0 root netem delay 100ms

• Add Packet Loss:

  sudo tc qdisc add dev eth0 root netem loss 10%

• Limit Bandwidth:

  sudo tc qdisc add dev eth0 root tbf rate 1mbit burst 32kbit latency 400ms

• Remove Rules:

  sudo tc qdisc del dev eth0 root

---

10. Analyze SSL/TLS Certificates with openssl

• Purpose: Check SSL/TLS certificates and connections.
• Command:

  openssl s_client -connect google.com:443

• Advanced Options:
  • Check certificate expiration:

    openssl s_client -connect google.com:443 2>/dev/null | openssl x509 -noout -dates

  • Test specific TLS version:

    openssl s_client -connect google.com:443 -tls1_2

---

11. Automate Network Tasks with expect

• Purpose: Automate interactive network commands (e.g., SSH, Telnet).
• Example Script:

  #!/usr/bin/expect
  spawn ssh [email protected]
  expect "password:"
  send "your_password\r"
  interact

• Save and run:

  ./script.exp

---

12. Test Network Throughput with netcat

• Purpose: Measure raw network throughput.
• Server Side:

  nc -l -p 5000 > /dev/null

• Client Side:

  dd if=/dev/zero bs=1M count=100 | nc <server_ip> 5000

---

13. Analyze Network Flows with nfdump

• Purpose: Analyze NetFlow data.
• Command:

  nfdump -r <flow_file>

• Advanced Options:
  • Filter by IP:

    nfdump -r <flow_file> 'host 192.168.1.1'

---

14. Check Bandwidth Usage

• Command: iftop -i eth0
• Purpose: Monitor real-time bandwidth usage.

Monitor Network Traffic with iftop

• Purpose: Real-time bandwidth monitoring.
• Command:

  sudo iftop -i eth0

• Advanced Options:
  • Filter by IP:

    sudo iftop -F 192.168.1.0/24 -i eth0

  • Display port numbers:

    sudo iftop -P -i eth0

---

15. Test HTTP Connectivity

• Command: curl -I <https://<url>

• Purpose: Test HTTP/HTTPS connectivity and fetch web content.

• Example:

  Fetch full content:

  curl https://google.com

---

Capture HTTP Traffic with ngrep

• Purpose: Filter and capture HTTP traffic.
• Command:

  sudo ngrep -d eth0 -W byline "GET|POST"

• Advanced Options:
  • Capture HTTPS traffic (decrypt with SSL key):

    sudo ngrep -d eth0 -W byline -q "GET|POST" port 443
    

16. Check ARP Table

• Command: arp -a
• Purpose: Display the ARP table (IP to MAC address mappings).

---

17. Restart Network Service

• Command: sudo systemctl restart networking
• Purpose: Restart the network service to apply changes.

---

18. Check Network Speed

• Command: speedtest-cli
• Purpose: Test internet speed.

---

19. Check Firewall Rules

• Command: sudo ufw status or sudo iptables -L
• Purpose: Display firewall rules.

---

20. Check Network Latency

• Command: mtr <URL>
• Purpose: Combine ping and traceroute to measure latency.

Analyze Network Latency with mtr

• Purpose: Combine ping and traceroute for advanced latency analysis.
• Command:

  mtr --report <target>

• Advanced Options:
  • Set packet size:

    mtr --psize 128 <target>

  • Use TCP instead of ICMP:

    mtr --tcp <target>

---

21. Check SSH Connectivity

• Command: ssh user@<ipv4 IP address>
• Purpose: Connect to a remote server via SSH.

Create a Network Tunnel with ssh*

• Purpose: Securely forward traffic through an SSH tunnel.
• Command:

  ssh -L <local_port>:<remote_host>:<remote_port> user@<ssh_server>

• Example: Forward local port 8080 to google.com:80 via an SSH server:

  ssh -L 8080:google.com:80 [email protected]

• Access google.com locally via http://localhost:8080.

---

22. Check Network Statistics

• Command: netstat -s
• Purpose: Display network statistics (e.g., packets, errors).

---

23. Check MAC Address

• Command: ip link show
• Purpose: Display MAC addresses of network interfaces.