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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Eventually, the specification for Internet Protocol, Version 6 (<strong>IP</strong>v6) was produced<br />

in RFC2460 as the latest version.<br />

9.1.2 <strong>IP</strong>v6 feature overview<br />

<strong>IP</strong>v6 offers the following significant features:<br />

► A dramatically larger address space, which is said to be sufficient for at least<br />

the next 30 years<br />

► Globally unique <strong>and</strong> hierarchical addressing, based on prefixes rather than<br />

address classes, to keep routing tables small <strong>and</strong> backbone routing efficient<br />

► A mechanism for the auto-configuration of network interfaces<br />

► Support for encapsulation of itself <strong>and</strong> other protocols<br />

► Class of service that distinguishes types of data<br />

► Improved multicast routing support (in preference to broadcasting)<br />

► Built-in authentication <strong>and</strong> encryption<br />

► Transition methods to migrate from <strong>IP</strong>v4<br />

► Compatibility methods to coexist <strong>and</strong> communicate with <strong>IP</strong>v4<br />

Note: <strong>IP</strong>v6 uses the term packet rather than datagram. The meaning is the<br />

same, although the formats are different.<br />

<strong>IP</strong>v6 uses the term node for any system running <strong>IP</strong>v6, that is, a host or a<br />

router. An <strong>IP</strong>v6 host is a node that does not forward <strong>IP</strong>v6 packets that are not<br />

explicitly addressed to it. A router is a node that forwards <strong>IP</strong> packets not<br />

addressed to it.<br />

9.2 The <strong>IP</strong>v6 header format<br />

The format of the <strong>IP</strong>v6 packet header has been simplified from its counterpart in<br />

<strong>IP</strong>v4. The length of the <strong>IP</strong>v6 header increases to 40 bytes (from 20 bytes) <strong>and</strong><br />

contains two 16-byte addresses (source <strong>and</strong> destination), preceded by 8 bytes of<br />

control information, as shown in Figure 9-2 on page 331. The <strong>IP</strong>v4 header has<br />

two 4-byte addresses preceded by 12 bytes of control information <strong>and</strong> possibly<br />

followed by option data. The reduction of the control information <strong>and</strong> the<br />

elimination of options in the header for most <strong>IP</strong> packets are intended to optimize<br />

the processing time per packet in a router. The infrequently used fields that have<br />

been removed from the header are moved to optional extension headers when<br />

they are required.<br />

330 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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