Справочник по сетевым протоколам


a PPP packet with an

Reception of a PPP packet with an unknown Protocol field indicates

that the peer is attempting to use a protocol which is

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

a Protocol-Reject.

Upon reception of a Protocol-Reject, the implementation MUST stop

sending packets of the indicated protocol at the earliest


Protocol-Reject packets can only be sent in the LCP Opened state.

Protocol-Reject packets received in any state other than the LCP

Opened state SHOULD be silently discarded.

A summary of the Protocol-Reject packet format is shown below. The

fields are transmitted from left to right.

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1


| Code | Identifier | Length |


| Rejected-Protocol | Rejected-Information ...



8 for Protocol-Reject.


The Identifier field MUST be changed for each Protocol-Reject



The Rejected-Protocol field is two octets, and contains the PPP

Protocol field of the packet which is being rejected.

Simpson [Page 35]

RFC 1661 Point-to-Point Protocol July 1994


The Rejected-Information field contains a copy of the packet which

is being rejected. It begins with the Information field, and does

not include any Data Link Layer headers nor an FCS. The

Rejected-Information MUST be truncated to comply with the peer's

established MRU.

5.8. Echo-Request and Echo-Reply


LCP includes Echo-Request and Echo-Reply Codes in order to provide

a Data Link Layer loopback mechanism for use in exercising both

directions of the link. This is useful as an aid in debugging,

link quality determination, performance testing, and for numerous

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