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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Fault management<br />

The LMP fault management procedure is based on a ChannelStatus message<br />

exchange that uses the following messages:<br />

► The ChannelStatus message is sent unsolicited <strong>and</strong> is used to notify an LMP<br />

neighbor about the status of one or more data channels of a TE link.<br />

► The ChannelStatusAck message is used to acknowledge receipt of the<br />

ChannelStatus message.<br />

► The ChannelStatusRequest message is used to query an LMP neighbor for<br />

the status of one or more data channels of a TE link.<br />

► The ChannelStatusResponse message is used to acknowledge receipt of the<br />

ChannelStatusRequest message <strong>and</strong> indicate the states of the queried data<br />

links.<br />

Control channel<br />

A control channel transports the reservation <strong>and</strong> routing information for traffic<br />

path setup:<br />

► To establish a control channel, the destination <strong>IP</strong> address on the far end of<br />

the control channel must be known. This knowledge can be manually<br />

configured or automatically discovered.<br />

► Control channels exist independently of TE links <strong>and</strong> multiple control<br />

channels can be active simultaneously between a pair of nodes. Individual<br />

control channels can be realized in different ways; one might be implemented<br />

in-fiber while another one might be implemented out-of-fiber.<br />

► There are four LMP messages used to manage individual control channels:<br />

– Config (Configuration)<br />

– ConfigAck (Positive acknowledgement)<br />

– ConfigNack (Negative Acknowledgement)<br />

– Hello messages<br />

► Control channel activation begins with a parameter negotiation exchange<br />

using Config, ConfigAck, <strong>and</strong> ConfigNack messages. The contents of these<br />

messages are built using LMP objects.<br />

► LMP uses a “Hello” protocol to send “Hello packets” exchanges over each<br />

control channel to maintain LMP connectivity. The LMP Hello protocol is<br />

intended to be a lightweight keepalive mechanism that will react to control<br />

channel failures rapidly so that IGP Hellos are not lost <strong>and</strong> the associated<br />

link-state adjacencies are not removed unnecessarily.<br />

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

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