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PPP can terminate the link

of LCP, NCP, and network-layer protocol packets.

3.7. Link Termination Phase

PPP can terminate the link at any time. This might happen because of

the loss of carrier, authentication failure, link quality failure,

the expiration of an idle-period timer, or the administrative closing

of the link.

LCP is used to close the link through an exchange of Terminate

packets. When the link is closing, PPP informs the network-layer

protocols so that they may take appropriate action.

After the exchange of Terminate packets, the implementation SHOULD

signal the physical-layer to disconnect in order to enforce the

termination of the link, particularly in the case of an

authentication failure. The sender of the Terminate-Request SHOULD

disconnect after receiving a Terminate-Ack, or after the Restart

counter expires. The receiver of a Terminate-Request SHOULD wait for

the peer to disconnect, and MUST NOT disconnect until at least one

Restart time has passed after sending a Terminate-Ack. PPP SHOULD

proceed to the Link Dead phase.

Any non-LCP packets received during this phase MUST be silently


Simpson [Page 9]

RFC 1661 Point-to-Point Protocol July 1994

Implementation Note:

The closing of the link by LCP is sufficient. There is no need

for each NCP to send a flurry of Terminate packets. Conversely,

the fact that one NCP has Closed is not sufficient reason to cause

the termination of the PPP link, even if that NCP was the only NCP

currently in the Opened state.

Simpson [Page 10]

RFC 1661 Point-to-Point Protocol July 1994

4. The Option Negotiation Automaton

The finite-state automaton is defined by events, actions and state

transitions. Events include reception of external commands such as

Open and Close, expiration of the Restart timer, and reception of

packets from a peer. Actions include the starting of the Restart

timer and transmission of packets to the peer.

Some types of packets -- Configure-Naks and Configure-Rejects, or

Code-Rejects and Protocol-Rejects, or Echo-Requests, Echo-Replies and

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