In
the link establishment and configuration negotiation phase, each PPP
device sends LCP packets to configure and establish the data link.
LCP packets contain a configuration option field that allows devices to negotiate the use of options, such as the maximum transmission unit (MTU), compression of certain PPP fields, and the link authentication protocol. If a configuration option is not included in an LCP packet, the default value for that configuration option is assumed.
Before any network-layer datagrams (for
example, IP) can be exchanged, LCP must first open the connection and
negotiate the configuration parameters. This phase is complete when a
configuration acknowledgment frame has been sent and received.
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