RFC 791 - Internet Protocol (IP)
The foundation of internet addressing and routing
What is IP?
The Internet Protocol (IP) is the principal communications protocol in the Internet Protocol Suite for relaying datagrams across network boundaries. It provides the addressing system that enables data to be routed between devices on different networks.
Key Features
Addressing
Provides unique IP addresses to identify devices on networks worldwide.
Routing
Enables packets to find their way across multiple networks to reach destinations.
Fragmentation
Breaks large packets into smaller fragments when crossing networks with different MTUs.
Best Effort
Provides unreliable, connectionless delivery - reliability is handled by higher layers.
IPv4 Header Structure
The IP header contains essential routing and delivery information:
- Version: IP version (4 for IPv4)
- Header Length: Size of IP header
- Type of Service: Quality of service indicators
- Total Length: Size of entire IP packet
- Identification: Unique packet identifier for fragmentation
- Flags: Fragmentation control
- Fragment Offset: Position of fragment in original packet
- Time to Live (TTL): Maximum hops before packet is discarded
- Protocol: Next layer protocol (TCP=6, UDP=17)
- Header Checksum: Error detection for header
- Source/Destination Address: 32-bit IP addresses
IP Addressing
IPv4 uses 32-bit addresses, typically written in dotted decimal notation:
- Class A: 1.0.0.0 to 126.255.255.255 (large networks)
- Class B: 128.0.0.0 to 191.255.255.255 (medium networks)
- Class C: 192.0.0.0 to 223.255.255.255 (small networks)
- Private Ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
- Loopback: 127.0.0.0/8 (localhost)
Routing Fundamentals
IP routing determines the path packets take through networks:
- Routing Tables: Store network destinations and next-hop information
- Default Gateway: Router for packets destined outside local network
- Subnet Masks: Determine network and host portions of addresses
- CIDR: Classless Inter-Domain Routing for efficient address allocation
IP in AWS Architecture
IP addressing is fundamental to AWS networking:
- VPC CIDR Blocks: Define IP address ranges for virtual networks
- Subnet Design: Allocate IP ranges within availability zones
- Elastic IPs: Static public IP addresses for AWS resources
- Route Tables: Control IP traffic routing within VPCs
- NAT Gateways: Enable private subnet internet access
- Security Groups: IP-based access control rules
- Load Balancers: Distribute traffic across multiple IP addresses
Modern Challenges & Solutions
IPv4 Address Exhaustion
Problem: Limited 32-bit address space
Solutions: NAT, CIDR, IPv6 adoption
Security
Problem: No built-in authentication or encryption
Solutions: IPSec, VPNs, application-layer security
Quality of Service
Problem: Best-effort delivery only
Solutions: DSCP markings, traffic shaping, QoS policies