CSCI 465Data Communications and Networks

Lecture 25

Martin van Bommel

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IP Versions

• 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

(IP Next Generation)

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Why Change IP Versions?• Address space exhaustion:– 2 level addressing (network and host) wastes space– IP network addresses used even if not connected

• Growth of networks and the Internet– extended use of TCP/IP – e.g. TV, point-of-sale– single address per host not flexible

• Requirements for new types of service– address configuration

• Routing flexibility - traffic support

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IPv6 Enhancements

• expanded 128 bit address space• improved option mechanism– most not examined by intermediate routes

• dynamic address assignment• increased addressing flexibility– unicast, anycast, and multicast

• support for resource allocation• labeled packet flows

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5

IPv6PDU

(Packet) Structure

IPv6 Header

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IP v6 Flow Label

• related sequence of packets - special handling– identified by source and destination address +

flow label– flow number generated randomly• make sure not to reuse within lifetime of old flow

• router treats packets of flow the same– treatment pre-negotiated with router(s)

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IPv6 Addresses

• 128 bits long– Assigned to interface– Same interface may have multiple addresses

• Types of addresses– Unicast – single interface address– Anycast – one of a set of interface addresses– Multicast – all of a set of interface addresses

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Hop-by-Hop Options

• must be examined by every router– if unknown discard/forward handling is specified

• next header – type of header that follows• header extension length – length of this header• Options– Jumbo payload

• IPv6 packet is longer than 65,535 octets

– Router alert• Tells router(s) that packet contains router control data

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Fragmentation Header

• fragmentation only allowed at source• no fragmentation at intermediate routers• node must perform path discovery to find

smallest MTU (maximum transmission unit) of intermediate networks

• set source fragments to match MTU• otherwise limit to 1280 octets– minimum MTU must be supported by networks

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Routing Header• contains a list of one or more intermediate nodes

to be visited on the way to a packet’s destination• Includes– Next header identification, Header length, Routing type– Segments left – number of route segments left

• Type 0 routing – IPv6 header has address of router– Routing header contains list of router addresses– Next destination address first on list– Final destination address last on list– Each router on path moves address to IPv6 header and shortens

list

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IPv6 Extension Headers

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