TCP vs UDP: What’s the Difference?

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are fundamental protocols for internet communication, each with distinct characteristics:

• TCP: Connection-oriented, reliable, and ensures ordered data delivery. Ideal for HTTP/HTTPS, FTP, and email (SMTP).
• UDP: Connectionless, low-latency, but no delivery guarantees. Used in VoIP, video streaming, and DNS queries.

You Should Know:

1. TCP in Action

• Establishing a TCP Connection (3-Way Handshake):

  Use tcpdump to capture the SYN, SYN-ACK, ACK process:
  sudo tcpdump -i eth0 'tcp[bash] & (tcp-syn|tcp-ack) != 0'
  

• Testing TCP Connectivity:

  nc -zv example.com 80  Check if port 80 (HTTP) is open
  

2. UDP in Action

• Sending UDP Packets:

  echo "Test UDP" | nc -u example.com 53  Send UDP to DNS port
  

• Capturing UDP Traffic:

  sudo tcpdump -i eth0 udp port 53  Monitor DNS queries
  

3. Protocol Selection Guide

• Use TCP for:
• Web servers (nginx/apache).
• Secure file transfers (scp/sftp).
• Use UDP for:
• Real-time apps (Zoom/RTP).
• Gaming servers (Unity/Unreal).

4. Linux Kernel Tweaks

• Increase TCP Buffer Size:

  sysctl -w net.ipv4.tcp_rmem="4096 87380 16777216"
  sysctl -w net.ipv4.tcp_wmem="4096 65536 16777216"
  

• Enable UDP Fast Open:

  sysctl -w net.ipv4.tcp_fastopen=3
  

What Undercode Say:

• TCP’s reliability comes at the cost of overhead (headers, retransmissions).
• UDP sacrifices reliability for raw speed—critical for latency-sensitive apps.
• Advanced Tools:
• Wireshark: Filter with tcp.port == 443 || udp.port == 53.
• iperf3: Test throughput (-u flag for UDP):

  iperf3 -s  Server 
  iperf3 -c server_ip -u -b 1G  Client (UDP flood test) 
  

• Windows CMD:

  Test-NetConnection -ComputerName example.com -Port 80  PowerShell TCP check
  

Expected Output:

 TCP 3-Way Handshake Capture (tcpdump):
20:10:00.123 IP client.12345 > server.80: Flags [bash], seq 123456789 
20:10:00.124 IP server.80 > client.12345: Flags [S.], seq 987654321, ack 123456790 
20:10:00.125 IP client.12345 > server.80: Flags [.], ack 987654322 

 UDP DNS Query (tcpdump):
20:10:05.678 IP client.54321 > 8.8.8.8.53: UDP, length 32 

Relevant Links:

• TCP RFC 793
• UDP RFC 768

References:

Reported By: Nasir Amin – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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