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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Record routes Record the route per count hop.<br />

Time stamp Time stamp each count hop.<br />

Endless ping Ping until manually stopped.<br />

Resolve address Resolve the host address to the host name.<br />

Time to Live (TTL) The time (in seconds) the datagram is allowed to travel.<br />

Type of Service (TOS) The type of internet service quality.<br />

Host-list Loose source route or strict source route of host lists.<br />

Timeout The timeout to wait for each reply.<br />

No fragmentation The fragment flag is not set.<br />

Ping uses the ICMP Echo <strong>and</strong> Echo Reply messages (refer to “Echo (8) <strong>and</strong><br />

Echo Reply (0)” on page 111). Because ICMP is required in every <strong>TCP</strong>/<strong>IP</strong><br />

implementation, hosts do not require a separate server to respond to ping<br />

requests.<br />

Ping is useful for verifying an <strong>IP</strong> installation. The following variations of the<br />

comm<strong>and</strong> each require the operation of an different portion of an <strong>IP</strong> installation:<br />

► ping loopback: Verifies the operation of the base <strong>TCP</strong>/<strong>IP</strong> software.<br />

► ping my-<strong>IP</strong>-address: Verifies whether the physical network device can be<br />

addressed.<br />

► ping a-remote-<strong>IP</strong>-address: Verifies whether the network can be accessed.<br />

► ping a-remote-host-name: Verifies the operation of the name server (or the<br />

flat namespace resolver, depending on the installation).<br />

Traceroute<br />

The Traceroute program is used to determine the route <strong>IP</strong> datagrams follow<br />

through the network.<br />

Traceroute is based on ICMP <strong>and</strong> UDP. It sends an <strong>IP</strong> datagram with a TTL of 1<br />

to the destination host. The first router decrements the TTL to 0, discards the<br />

datagram, <strong>and</strong> returns an ICMP Time Exceeded message to the source. In this<br />

way, the first router in the path is identified. This process is repeated with<br />

successively larger TTL values to identify the exact series of routers in the path<br />

to the destination host.<br />

Traceroute sends UDP datagrams to the destination host. These datagrams<br />

reference a port number outside the st<strong>and</strong>ard range. When an ICMP Port<br />

Unreachable message is received, the source determines the destination host<br />

has been reached.<br />

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

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