UDP

User Datagram Protocol is a fast, connectionless transport protocol.

UDP Basics

Connectionless: No connection setup required
Stateless: No connection state maintained
Unreliable: No delivery guarantee
Fast: Minimal overhead
Datagram-based: Fixed-size packets

When to Use UDP

Perfect For

Live video/audio streaming
Online gaming
VoIP (Voice over IP)
DNS queries
DHCP
NTP (Network Time Protocol)
Real-time applications

Why UDP?

Speed is critical
Occasional packet loss acceptable
Low latency required
Many simultaneous connections

UDP Packet Structure

Source Port (16 bits)
Destination Port (16 bits)
Length (16 bits)
Checksum (16 bits)
[Data/Payload]

Common UDP Ports

53 - DNS
67, 68 - DHCP
123 - NTP
161, 162 - SNMP
514 - Syslog
1900 - UPnP
5353 - mDNS

UDP vs TCP

UDP                    TCP
No connection setup    3-way handshake
No delivery guarantee  Reliable delivery
Out of order possible  In-order delivery
Low overhead          Higher overhead
Faster                Slower
Connectionless        Connection-oriented

Python UDP Example

Server

import socket

server = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
server.bind(('localhost', 5000))

while True:
    data, addr = server.recvfrom(1024)
    print(f"Received from {addr}: {data}")
    server.sendto(b"Echo: " + data, addr)

Client

import socket

client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
client.sendto(b"Hello", ('localhost', 5000))
response, _ = client.recvfrom(1024)
print(response)

Network Tools for UDP

# Send UDP packets
nc -u host port
echo "message" | nc -u localhost 5000

# Monitor UDP traffic
tcpdump -i eth0 'udp port 53'

# Check open UDP ports
sudo ss -ulnp

# DNS queries use UDP
nslookup example.com
dig example.com

# DHCP uses UDP
dnsmasq # DHCP server
dhclient # DHCP client

Real-World Applications

DNS (Port 53)

Domain name to IP address resolution
Uses UDP for queries
Falls back to TCP for large responses

DHCP (Ports 67, 68)

Automatic IP address assignment
Client broadcasts to find server
Server responds with IP configuration

NTP (Port 123)

Network Time Protocol
Synchronize system clocks
Critical for logging and security

Syslog (Port 514)

Remote logging
Send logs to central server
Important for monitoring

Best Practices

Use UDP only when appropriate
Implement application-level reliability if needed
Monitor packet loss
Test with various network conditions
Use checksums for verification
Implement timeouts
Monitor UDP traffic for security
Don't use for critical data

UDP

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