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IPv6 Specification

This article discusses the header fields and format of IPv6, comparing it to IPv4 and highlighting the benefits and improvements of IPv6. It also covers the traffic class, flow labels, extension headers, and fragmentation.

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IPv6 Specification

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  1. IPv6 Specification Ankit Amin Saurabh Patel

  2. IPv4 Header Format

  3. Header Fields • Version • Internet header length • In 32 bit words • Including options • Type of service • Total length • Of datagram, in octets • Identification • Sequence number • Used with addresses and user protocol to identify datagram uniquely

  4. Header Fields • Flags • More bit, Don’t fragment • Fragmentation offset • Time to live • Protocol • Next higher layer to receive data field at destination • Header checksum • Source address, Destination address • Options and Padding • To fill to multiple of 32 bits long

  5. IPv6 vs. IPv4 • Expanded Addressing Capabilities • 32 bits to 128 bits • Header Format Simplification • Drop in IPv4 header fields to be cost effective. • Improved Support for Extensions and Options • Efficient forwarding, less stringent limits on length of options and greater flexibility for introducing new options in the future. • Flow Labeling Capability • Special handling of packets. • Authentication and Privacy Capabilities • Header Size is 60 for IPv6 and 40 for IPv4 with TCP len.

  6. IPv6 Header

  7. Traffic Class • 8-bit field • Used by the source and intermediate nodes to identify between classes and priorities of packets. • Still under development. • How can we differentiate between services that IP packets needs?

  8. Flow Labels • 20 bit field • It is used to label sequences of packets for special handling by IPv6 routers • Non-default QoS • Real-time service • Still in experimental stage: subject to change depending on Internet flow control.

  9. Extension Header Options • IPv6 • Hop-by-Hop options • Destination options • Routing • Fragment • Authentication* • Encapsulating Security Payload* • Upper-layer *Note: These options are not discussed in this RFC 2460: IPv6 Specification.

  10. Hop-by-Hop Options • It is used to carry optional information that is examined by every node along the packet’s delivery path. • Is identified by the Next Header value of 0. • Each packet is tagged with hop limit. Why?

  11. Hop-by-Hop option fields • Next header • Header extension length • Options • Jumbo payload • Over 216 = 65,535 octets

  12. Destination Options • It is used to carry optional information that needs to be examined by destination node. • Same format as Hop-by-Hop options header • Occurs once before Routing and once before upper layer header.

  13. Routing Header • It is used to list intermediate nodes to be visited on the way to a packet’s destination. • Next Header value is 43. • It is very similar to IPv4’s Loose Source and record Route option. • Fields • Next Header • Header extension length • Routing type • Segments left • Number of nodes still to be visited • Type-specific data

  14. Type 0 Routing header • Next Header • Header Extension Length • Routing Type =0 • Segments Left • Reserved = 0 for transmission • Address[1..n]

  15. Fragmentation Header • Fragmentation only allowed at source • No fragmentation at intermediate routers • Node must perform path discovery to find smallest MTU of intermediate networks • Source fragments to match MTU • Otherwise limit to 1280 octets • According to authors reassembly is abandon after 60 secs.

  16. Fragmentation Header Fields • Next Header • Reserved • Fragmentation offset • Reserved • More flag • Identification

  17. Upper-Layer • Upper-layer checksum • Any transport/upper layer protocol must be modified to be used in 128 bit addresses. • Unlike IPv4, UDP checksum is not optional under IPv6

  18. Questions??

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