TCP/IP

TCP/IP is the fundamental protocol suite that powers the modern internet.

What is TCP/IP?

TCP/IP is a four-layer model:

Application Layer: HTTP, HTTPS, FTP, SSH, DNS, SMTP
Transport Layer: TCP, UDP
Internet Layer: IP (IPv4, IPv6), ICMP
Link Layer: Ethernet, WiFi

IP (Internet Protocol)

Handles routing and addressing

IPv4

• 32-bit addresses
• Format: 192.168.1.1
• Approximately 4.3 billion addresses
• Most common today

IPv6

• 128-bit addresses
• Format: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
• Virtually unlimited addresses
• Future standard

TCP (Transmission Control Protocol)

Reliable, connection-oriented transmission

Connection Establishment (Three-Way Handshake)

1. Client sends SYN
2. Server responds with SYN-ACK
3. Client sends ACK
→ Connection established

Characteristics

• Reliable delivery
• In-order delivery
• Flow control
• Error checking
• Connection-oriented

When to Use TCP

• Email (SMTP, POP3)
• Web (HTTP, HTTPS)
• File transfer (FTP, SFTP)
• Remote access (SSH, Telnet)
• Database connections

UDP (User Datagram Protocol)

Fast, connectionless transmission

Characteristics

• No guarantee of delivery
• May arrive out of order
• Low overhead
• Fast transmission
• Connectionless

When to Use UDP

• Video streaming
• Audio streaming
• Online gaming
• DNS queries
• DHCP
• Real-time applications

TCP vs UDP

TCP:              UDP:
Reliable          Unreliable
Ordered           Unordered
Slower            Faster
Connectionful     Connectionless
Error checking    Minimal checking

ICMP (Internet Control Message Protocol)

Used for diagnostics and error reporting

Common Uses

# Ping (ICMP Echo)
ping example.com

# Traceroute (ICMP Time Exceeded)
traceroute example.com

# Check connectivity
ping -c 4 8.8.8.8

Network Tools

# View network configuration
ifconfig
ip addr

# Check connectivity
ping 8.8.8.8
nslookup example.com

# View routing table
route -n
ip route

# View active connections
ss -tuln
netstat -tuln

# Trace route to destination
traceroute example.com
mtr example.com

# Monitor network traffic
tcpdump
wireshark

Best Practices

• Use TCP for data integrity
• Use UDP for speed where loss acceptable
• Monitor network performance
• Understand your protocol needs
• Test connectivity regularly
• Keep router/firewall updated
• Monitor bandwidth usage