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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Network Interface Layer (OSI Data Link Layer) Protocols
           9  TCP/IP Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP)
                9  Point-to-Point Protocol (PPP)
                     9  PPP Fundamentals and Operation

Previous Topic/Section
PPP Components and General Operation
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Pages in Current Topic/Section
12
3
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PPP Standards
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PPP Link Setup and Phases
(Page 3 of 3)

Differentiating LCP and NCP Links

Remember that the basic link is established by LCP, and NCP links are set up within the LCP link. Closing an NCP link does not cause the LCP link to be closed. Even if all NCPs are closed, the LCP link remains open. (Of course, no data can be passed until an appropriate NCP link is re-established; a device is required to discard frames received containing any layer three protocol that does not have an opened NCP.) To terminate a PPP connection, only the LCP link needs to be terminated in the Link Termination phase; the NCPs do not need to be explicitly closed.

PPP Link Setup and Phase Summary

A summary of PPP phases can be found in Table 24. In the table, the LCP Link Status and NCP Link Status columns show the status of the link as the phase starts.


Table 24: PPP Phases

Phase/
State

Phase Summary

LCP Link Status Upon Entry To Phase

NCP Link Status Upon Entry To Phase

Transition Requirement

Transition To Phase

Link Dead

Default state; physical layer not connected.

Closed

Closed

Successful
physical layer connection

Link Establishment

Link Establishment

Physical layer connected, basic configuration of link performed by LCP.

Closed

Closed

Successful
negotiation

Authentication

Unsuccessful negotiation

Link Dead

Authentication

Basic link is now opened, and optional authentication of device is performed.

Open

Closed

Successful authentication or no authentication required

Network-Layer Protocol

Unsuccessful authentication

Link Termination

Network-Layer Protocol

One or more NCPs open an NCP link within the LCP link.

Open

Closed

All NCPs opened

Link Open

Link Open

Link is open and operating normally.

Open

Open

Link failure or close request

Link Termination

Link Termination

LCP link is shut down.

Open

Open

 

Link Dead


Previous Topic/Section
PPP Components and General Operation
Previous Page
Pages in Current Topic/Section
12
3
Next Page
PPP Standards
Next Topic/Section

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