This document specifies the Internet Protocol, Version 6 (IPv6), which is the next generation of the Internet Protocol. IPv6 improves upon IPv4 by increasing the address size from 32 bits to 128 bits, simplifying the header format, enhancing support for extensions and options, and introducing flow labeling and authentication capabilities. The IPv6 header includes fields for traffic class, flow label, payload length, next header, hop limit, source and destination addresses. Extension headers allow for additional information to be carried, such as hop-by-hop options, routing, fragment, destination options, authentication, and encapsulating security payload. The order of extension headers is specified to ensure proper processing. Options within these headers are encoded in type-length-value format and must be processed in order. The hop-by-hop options header is examined by all nodes along the packet's path, while other headers are processed only at the destination. The document also discusses packet size issues, flow labels, traffic classes, and upper-layer protocol considerations. IPv6 requires that each link have an MTU of at least 1280 octets, and fragmentation is handled by the source node. The flow label field allows for special handling of packets, while the traffic class field is used to classify packets. Upper-layer protocols must be adjusted for IPv6, including checksums and packet lifetime. The document outlines the structure and semantics of IPv6 addresses, headers, and extension headers, as well as the handling of packets with routing headers. It also provides formatting guidelines for options and discusses security considerations.This document specifies the Internet Protocol, Version 6 (IPv6), which is the next generation of the Internet Protocol. IPv6 improves upon IPv4 by increasing the address size from 32 bits to 128 bits, simplifying the header format, enhancing support for extensions and options, and introducing flow labeling and authentication capabilities. The IPv6 header includes fields for traffic class, flow label, payload length, next header, hop limit, source and destination addresses. Extension headers allow for additional information to be carried, such as hop-by-hop options, routing, fragment, destination options, authentication, and encapsulating security payload. The order of extension headers is specified to ensure proper processing. Options within these headers are encoded in type-length-value format and must be processed in order. The hop-by-hop options header is examined by all nodes along the packet's path, while other headers are processed only at the destination. The document also discusses packet size issues, flow labels, traffic classes, and upper-layer protocol considerations. IPv6 requires that each link have an MTU of at least 1280 octets, and fragmentation is handled by the source node. The flow label field allows for special handling of packets, while the traffic class field is used to classify packets. Upper-layer protocols must be adjusted for IPv6, including checksums and packet lifetime. The document outlines the structure and semantics of IPv6 addresses, headers, and extension headers, as well as the handling of packets with routing headers. It also provides formatting guidelines for options and discusses security considerations.