IPv4 and IPv6 are two versions of Internet Protocol (IP) used for identifying devices on a network. Here are the main differences:

Address Format:

• IPv4: Uses a 32-bit address format, expressed in decimal as four octets separated by periods (e.g., 192.168.1.1). It supports about 4.3 billion unique addresses.
• IPv6: Uses a 128-bit address format, expressed in hexadecimal and separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). It supports a vastly larger number of unique addresses.

Address Space:

• IPv4: Limited address space, leading to the exhaustion of available addresses.
• IPv6: Provides an enormous address space, effectively eliminating the issue of address exhaustion.

Header Complexity:

• IPv4: More complex header with 12 fields, making it less efficient for routing.
• IPv6: Simplified header with 8 fields, designed for efficient processing and routing.

Configuration:

• IPv4: Often requires manual or DHCP configuration.
• IPv6: Supports auto-configuration capabilities, allowing devices to generate their own addresses.

Security:

• IPv4: Security is optional and relies on additional protocols like IPsec.
• IPv6: IPsec is built-in, providing mandatory support for secure communications.

Fragmentation:

• IPv4: Routers and sending hosts can fragment packets.
• IPv6: Only sending hosts can fragment packets, enhancing efficiency and reducing router workload.

IPv6 improves scalability, security, and efficiency over IPv4, addressing the limitations of the older protocol.