LCP
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... PPP provides a Link Control Protocol
(LCP). The LCP is used to automatically agree upon the
encapsulation format ...
... Link Control Protocol
(LCP). The LCP is used to automatically agree upon the
encapsulation format options, handle varying limits on sizes of
...
... negotiation mechanism described in this
document is specified in terms of the Link Control Protocol (LCP),
the same facilities are designed to be used by other control
protocols, especially the family of NCPs ...
... end of the PPP link MUST first send LCP packets to configure and test
the data link. After the link ...
...
The link will remain configured for communications until explicit LCP
or NCP packets close the link ...
...
During this phase, the LCP automaton (described later) will be in the
Initial or Starting states. The transition to the Link Establishment
phase ...
... Initial or Starting states. The transition to the Link Establishment
phase will signal an Up event to the LCP automaton.
...
...
The Link Control Protocol (LCP) is used to establish the connection
through an exchange of Configure packets. This exchange is complete,
...
... connection
through an exchange of Configure packets. This exchange is complete,
and the LCP Opened state entered, once a Configure-Ack packet
(described later) has been both sent and received.
...
... All Configuration Options are assumed to be at default values unless
altered by the configuration exchange. See the chapter on LCP
Configuration Options for further discussion.
...
... independent of particular network-layer protocols are configured by
LCP. Configuration of individual network-layer protocols is handled
by separate Network Control Protocols ...
...
Any non-LCP packets received during this phase MUST be silently
discarded.
...
...
The receipt of the LCP Configure-Request causes a return to the Link
Establishment phase from the Network-Layer Protocol phase or
...
...
While LCP is in the Opened state, any protocol packet which is
unsupported by the implementation MUST be returned in a Protocol-
...
... link traffic consists of any possible combination
of LCP, NCP, and network-layer protocol packets.
...
...
Any non-LCP packets received during this phase MUST be silently
discarded.
...
...
The closing of the link by LCP is sufficient. There is no need
for each NCP to send a flurry of Terminate packets. Conversely,
...
... PPP link to the physical
media, to signal LCP that the link is entering Link Establishment
phase.
...
... Network-Layer Protocol phase. That is, the This-Layer-Up
action from LCP triggers the Up event in the NCP.
...
... Network-Layer Protocol phase. That is, the This-Layer-
Down action from LCP triggers the Down event in the NCP.
...
... link is administratively available (by
definition), this can be accomplished by simulating a Close
event to the LCP, immediately followed by an Open event. Care
must be taken that an intervening Close event cannot occur from
another source.
...
... The RXJ- event arises when the rejected value is catastrophic,
such as a Code-Reject of Configure-Request, or a Protocol-Reject
of LCP! This event communicates an unrecoverable error that
terminates the connection.
...
... state.
Typically, this action is used by the LCP to signal the Up event
to a NCP, Authentication Protocol ...
... state.
Typically, this action is used by the LCP to signal the Down event
to a NCP, Authentication Protocol ...
... layer has terminated.
Typically, this action MAY be used by the LCP to advance to the
Link Dead phase, or MAY be used by a NCP ...
... Link Dead phase, or MAY be used by a NCP to indicate to the LCP
that the link may terminate when there are no other NCPs ...
... Option, typically because it is not recognized or implemented.
The use of Configure-Nak versus Configure-Reject is more fully
described in the chapter on LCP Packet Formats.
...
... LCP Packet Formats ...
...
In the interest of simplicity, there is no version field in the LCP
packet. A correctly functioning LCP implementation will always
...
... version field in the LCP
packet. A correctly functioning LCP implementation will always
respond to unknown Protocols and Codes with an easily recognizable
LCP ...
... LCP implementation will always
respond to unknown Protocols and Codes with an easily recognizable
LCP packet, thus providing a deterministic fallback mechanism for
implementations of other versions.
...
... negotiated. In particular, each Configuration Option specifies a
default value. This ensures that such LCP packets are always
recognizable, even when one end of the link mistakenly believes the
...
... Code
The Code field is one octet, and identifies the kind of LCP
packet. When a packet is received with an unknown Code field, a
...
... Code-Reject packet is transmitted.
Up-to-date values of the LCP Code field are specified in the most
recent "Assigned Numbers" RFC [2]. This document concerns the
...
...
The Length field is two octets, and indicates the length of the
LCP packet, including the Code, Identifier, Length and Data
fields. The Length MUST NOT exceed the MRU ...
... Description
LCP includes Terminate-Request and Terminate-Ack Codes in order to
provide a mechanism for closing a connection.
...
... Description
Reception of a LCP packet with an unknown Code indicates that the
peer is operating with a different version. This MUST be reported
...
... Rejected-Packet
The Rejected-Packet field contains a copy of the LCP packet which
is being rejected. It begins with the Information field, and does
not include any Data Link Layer ...
... unsupported. This usually occurs when the peer attempts to
configure a new protocol. If the LCP automaton is in the Opened
state, then this MUST be reported back to the peer by transmitting ...
... opportunity.
Protocol-Reject packets can only be sent in the LCP Opened state.
Protocol-Reject packets received in any state ...
... state.
Protocol-Reject packets received in any state other than the LCP
Opened state SHOULD be silently discarded.
...
... Echo-Reply packets received in any
state other than the LCP Opened state SHOULD be silently
discarded.
...
... Description
LCP includes a Discard-Request Code in order to provide a Data
Link Layer sink mechanism for use in exercising the local to
remote direction of the link ...
... performance testing, and for numerous other functions.
Discard-Request packets MUST only be sent in the LCP Opened state.
On reception, the receiver ...
... LCP Configuration Options ...
...
LCP Configuration Options allow negotiation of modifications to the
default characteristics of a point-to-point link ...
...
The end of the list of Configuration Options is indicated by the
Length field of the LCP packet.
...
... The Type field is one octet, and indicates the type of
Configuration Option. Up-to-date values of the LCP Option Type
field are specified in the most recent "Assigned Numbers" RFC [2 ...
... during normal operation, as well as during Configuration Option
negotiation. All LCP Echo-Request, Echo-Reply, and Discard-
...
... Procedures for recovery from either case are unspecified, and may
vary from implementation to implementation. A somewhat
pessimistic procedure is to assume a LCP Down event. A further
Open event will begin the process of re-establishing the link,
...
...
The Protocol field is never compressed when sending any LCP
packet. This rule guarantees unambiguous recognition of LCP
...
... Protocol field is never compressed when sending any LCP
packet. This rule guarantees unambiguous recognition of LCP
packets.
...
... The Address and Control fields MUST NOT be compressed when sending
any LCP packet. This rule guarantees unambiguous recognition of
LCP packets.
...
... any LCP packet. This rule guarantees unambiguous recognition of
LCP packets.
When the Address ...