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Transcript
CSC 600 Internetworking with TCP/IP Unit 7: IPv6 (ch. 33) Dr. Cheer-Sun Yang Spring 2001 IP v6 - Version Number • • • • IP v 1-3 defined and replaced IP v4 - current version IP v5 - streams protocol IP v6 - replacement for IP v4 – During development it was called IPng – Next Generation Why Change IP? • New computer and communication technologies • New applications – VoIP requires real-time data delivery • Increase in size and load – too many hosts! Why Change IP? • Address space exhaustion – Two level addressing (network and host) wastes space – Network addresses used even if not connected to Internet – Growth of networks and the Internet – Extended use of TCP/IP – Single address per host • Requirements for new types of service Why Change IP? • New technologies : since 1970s, – processor performance has increased over two orders of magnitude – Memory sizes have increased by over a factor of 100 – Network bandwidth of the Internet backbone has risen by a factor of 7000 – LAN technologies have emerged • Increase in size – the number of hosts has risen from a handful to 56 million; the current 32-bit IP address space cannot accommodate projected growth of the global Internet beyond 2002. IPv6 RFCs • 1752 - Recommendations for the IP Next Generation Protocol • 2460 - Overall specification • 2373 - addressing structure • Others : 2462, 2463, 2464, 2374, 2375, 2526, etc. IPv6 Enhancements (1) • Expanded address space – 128 bit • Improved option mechanism – Separate optional headers between IPv6 header and transport layer header – Most are not examined by intermediate routes • Improved speed and simplified router processing • Easier to extend options • Address autoconfiguration – Dynamic assignment of addresses IPv6 Enhancements (2) • Increased addressing flexibility – Anycast - delivered to one of a set of nodes – Improved scalability of multicast addresses • Support for resource allocation – – – – Replaces type of service Labeling of packets to particular traffic flow Allows special handling e.g. real time video Structure Base Header • Alignment has been changed from 32-bit to 64-bit multiples. • The header length has been eliminated and the datagram length field has been replaced by a PAYLOAD LENGTH field. • The size of source and destination address fields has been increased to 16 octets each. Base Header (cont’d) • Fragmentation information has been removed out of fixed fields into an extension header. • The TIME-TO-LIVE field has been rep[laced by a HOP LIMIT field. • The SERVICE TYPE is renamed to be a TRAFFIC CLASS field, and extended with a FLOW LABEL field. • The PROTOCOL field has been replaced by the type of the next header. Extension Headers • Hop-by-Hop Options – Require processing at each router • Routing – Similar to v4 source routing • • • • Fragment Authentication Encapsulating security payload Destination options – For destination node Extension Headers (cont’d) • IPv6 extension headers are similar to IPv4 options. Each datagram includes extension headers for only those facilities that the datagram uses. IP v6 Header IP v6 Header Fields (1) • Version – 6 • Traffic Class – Classes or priorities of packet – Still under development – See RFC 2460 • Flow Label – Used by hosts requesting special handling • Payload length – Includes all extension headers plus user data IP v6 Header Fields (2) • Next Header – Identifies type of header • Extension or next layer up • Source Address • Destination address IPv6 Base Header From now on, they can’t call me Junior! 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 Fragmentation Header Fields • • • • • • Next Header Reserved Fragmentation offset Reserved More flag Identification End-to-End Fragmentation • An internet protocol that uses end-to-end fragmentation requires a sender to discover the path MTU to each destination, and to fragment any outgoing datagram that is larger than the path MTU. End-to-end fragmentation does not accommodate route changes. • To solve the problem of route changes that affect the path MTU, IPv6 includes a new ICMP error message. When a route discovers that fragmentation is needed, it sends the message back to the source. The source will fragment the datagrams based on the new minimum MTU. Source Routing Header • List of one or more intermediate nodes to be visited • Next Header • Header extension length • Routing type • Segments left – i.e. number of nodes still to be visited IPv6 Options Hop-by-Hop Options • Next header • Header extension length • Options – Jumbo payload • Over 216 = 65,535 octets – Router alert • Tells the router that the contents of this packet is of interest to the router • Provides support for RSPV (chapter 16) Destination Options • Same format as Hop-by-Hop options header IPv6 Addresses • 128 bits long • Assigned to interface • Single interface may have multiple unicast addresses • Three types of address Types of address • Unicast – Single interface • Anycast – Set of interfaces (typically different nodes) – Delivered to any one interface – the “nearest” • Multicast – Set of interfaces – Delivered to all interfaces identified Aggregatable Global Unicast Address Structure Interface Identifier Multicasting • Addresses that refer to group of hosts on one or more networks • Uses – – – – – Multimedia “broadcast” Teleconferencing Database Distributed computing Real time workgroups Group Membership in IPv6 • Multicast addresses are used to define a group of hosts instead of one. • All use the prefix 11111111 in the first field. • The second field is a flag that defines the group address as either permanent or transient. • The third field is a SCOPE field which indicates the scope to be node local(0001), link local (0010), site local(0101), organizational local (1000), or global(1110). ICMP v6 • Function of IGMP included in ICMP v6 • New group membership termination message to allow host to leave group