network protocols handbook.pdf

67Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NameIPv6: Internet Protocol version6Protocol DescriptionIPv6 is the new version of Internet Protocol (IP) based on IPv4,a network-layer (Layer 3) protocol that contains addressing informationand some control information enabling packets to berouted in the network. There are two basic IP versions: IPv4 andIPv6. IPv6 is also called next generation IP or IPng. IPv4 andIPv6 are de-multiplexed at the media layer. For example, IPv6packets are carried over Ethernet with the content type 86DD(hexadecimal) instead of IPv4’s 0800. This document describesthe IPv6 details. The IPv4 is described in a separate document.IPv6 increases the IP address size from 32 bits to 128 bits, tosupport more levels of addressing hierarchy, a much greaternumber of addressable nodes and simpler auto-configurationof addresses. IPv6 addresses are expressed in hexadecimalformat (base 16) which allows not only numerals (0-9) but afew characters as well (a-f). A sample ipv6 address looks like:3ffe:ffff:100:f101:210:a4ff:fee3:9566. Scalability of multicast addressesis introduced. A new type of address called an anycastaddress is also defined, to send a packet to any one of a groupof nodes. Two major improvements in IPv6 vs. v4:• Improved support for extensions and options - IPv6 optionsare placed in separate headers that are locatedbetween the IPv6 header and the transport layer header.Changes in the way IP header options are encodedallow more efficient forwarding, less stringent limits onthe length of options, and greater flexibility for introducingnew options in the future. The extension headersare: Hop-by-Hop Option, Routing (Type 0), Fragment,Destination Option, Authentication, and EncapsulationPayload.• Flow labeling capability - A new capability has been addedto enable the labeling of packets belonging to particulartraffic flows for which the sender requests specialhandling, such as non-default Quality of Service or realtimeservice.Protocol Structure4 12 16 24 32bitVersion Priority Flow labelPayload length Next header Hop limitSource address (128 bits)Destination address (128 bits)identify the desired delivery priority of the packets.Priority values are divided into ranges: traffic wherethe source provides congestion control and non-congestioncontrol traffic.• Flow label -- 20-bit flow label is used by a sourceto label those products for which it requests specialhandling by the IPv6 router. The flow is uniquely identifiedby the combination of a source address and anon-zero flow label.• Payload length -- 16-bit integer in octets is the lengthof payload including header.• Next header – 8-bit selector identifies the type ofheader immediately following the IPv6 header.• Hop limit -- 8-bit integer that is decremented by oneby each node that forwards the packet. The packet isdiscarded if the Hop Limit is decremented to zero.• Source address -- 128-bit address of the originator ofthe packet .• Destination address -- 128-bit address of the intendedrecipient of the packet (possibly not the ultimaterecipient, if a Routing header is present).Related protocolsIP, TCP, UDP, ICMP, SNMP, FTP, TELNET, SMTP, ARP, RARP,RPC, XDR, and NFSSponsor SourceIPv6 is defined by IETF (http://www.ietf.org) RFC 1883 (original)and RFC 2460 (latest).Referencehttp://www.javvin.com/protocol/rfc1883.pdfIPv6 Specifications (original)http://www.javvin.com/protocol/rfc2460.pdfIPv6 specifications (the latest)http://www.ipv6forum.comA good informational site• Version – 4-bit Internet Protocol Version number(IPv6 is 6).• Priority -- 8-bit traffic class field enables a source to