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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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3.1 Internet Protocol (<strong>IP</strong>)<br />

3.1.1 <strong>IP</strong> addressing<br />

<strong>IP</strong> is a st<strong>and</strong>ard protocol with STD number 5. The st<strong>and</strong>ard also includes ICMP<br />

(see 3.2, “Internet Control Message Protocol (ICMP)” on page 109) <strong>and</strong> IGMP<br />

(see 3.3, “Internet Group Management Protocol (IGMP)” on page 119). <strong>IP</strong> has a<br />

status of required.<br />

The current <strong>IP</strong> specification is in RFC 950, RFC 919, RFC 922, RFC 3260 <strong>and</strong><br />

RFC 3168, which updates RFC 2474, <strong>and</strong> RFC 1349, which updates RFC 791.<br />

Refer to 3.8, “RFCs relevant to this chapter” on page 140 for further details<br />

regarding the RFCs.<br />

<strong>IP</strong> is the protocol that hides the underlying physical network by creating a virtual<br />

network view. It is an unreliable, best-effort, <strong>and</strong> connectionless packet delivery<br />

protocol. Note that best-effort means that the packets sent by <strong>IP</strong> might be lost,<br />

arrive out of order, or even be duplicated. <strong>IP</strong> assumes higher layer protocols will<br />

address these anomalies.<br />

One of the reasons for using a connectionless network protocol was to minimize<br />

the dependency on specific computing centers that used hierarchical<br />

connection-oriented networks. The United States Department of Defense<br />

intended to deploy a network that would still be operational if parts of the country<br />

were destroyed. This has been proven to be true for the Internet.<br />

<strong>IP</strong> addresses are represented by a 32-bit unsigned binary value. It is usually<br />

expressed in a dotted decimal format. For example, 9.167.5.8 is a valid <strong>IP</strong><br />

address. The numeric form is used by <strong>IP</strong> software. The mapping between the <strong>IP</strong><br />

address <strong>and</strong> an easier-to-read symbolic name, for example, myhost.ibm.com, is<br />

done by the Domain Name System (DNS), discussed in 12.1, “Domain Name<br />

System (DNS)” on page 426.<br />

The <strong>IP</strong> address<br />

<strong>IP</strong> addressing st<strong>and</strong>ards are described in RFC 1166. To identify a host on the<br />

Internet, each host is assigned an address, the <strong>IP</strong> address, or in some cases, the<br />

Internet address. When the host is attached to more than one network, it is called<br />

multihomed <strong>and</strong> has one <strong>IP</strong> address for each network interface. The <strong>IP</strong> address<br />

consists of a pair of numbers:<br />

<strong>IP</strong> address = <br />

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

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