Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Enjoy The TCP/IP Guide? Get the complete PDF!
The TCP/IP Guide

Custom Search







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 Core Protocols: Link Control, Network Control and Authentication

Previous Topic/Section
PPP Core Protocols: Link Control, Network Control and Authentication
Previous Page
Pages in Current Topic/Section
12
3
Next Page
PPP Network Control Protocols (IPCP, IPXCP, NBFCP and others)
Next Topic/Section

PPP Link Control Protocol (LCP)
(Page 3 of 3)

LCP Link Maintenance

Once the link has been negotiated, LCP passes control to the appropriate authentication and/or NCP protocols as discussed in the PPP Link Setup and Phases topic. Eventually the link setup will complete and go into the open state. LCP messages can then be used by either device to manage or debug the link:

  • Code-Reject and Protocol-Reject: These frame types are used to provide feedback when one device receives an invalid frame due to either an unrecognized LCP Code (LCP frame type) or a bad Protocol identifier.

  • Echo-Request, Echo-Reply and Discard-Request: These frames can be used for testing the link.
LCP Link Termination

Finally, when the link is ready to be shut down, LCP terminates it. The device initiating the shutdown (which may not be the one that initiated the link in the first place) sends a Terminate-Request message. The other device replies back with a Terminate-Ack. A termination request indicates that the device sending it needs to close the link. Like a four-year-old who tells you he “needs to go now, bad!”, this is a request that cannot be denied. J

Other LCP Messages

The standard RFC 1570, PPP LCP Extensions, also defines two new LCP message types. The Identification message is used to allow a device to identify itself to its peer on the link. The Time-Remaining message lets one device tell the other how much time remains in the current session.

Relationship Between LCP and Other PPP Protocols

Note that many of the other protocols used in PPP are modeled after LCP. They use the same basic techniques for establishing protocol connections, and send and receive a subset of LCP message types. They also exchange configuration options in a similar manner. The next topic shows how the Network Control Protocols (NCPs) are based on LCP. You will see the same thing in looking at feature protocols such as CCP, ECP and others.


Previous Topic/Section
PPP Core Protocols: Link Control, Network Control and Authentication
Previous Page
Pages in Current Topic/Section
12
3
Next Page
PPP Network Control Protocols (IPCP, IPXCP, NBFCP and others)
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.