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RFC1661 - часть 6

least significant bit of the most significant octet equals "0".

Frames received which don't comply with these rules MUST be

treated as having an unrecognized Protocol.

Protocol field values in the "0***" to "3***" range identify the

network-layer protocol of specific packets, and values in the

"8***" to "b***" range identify packets belonging to the

associated Network Control Protocols (NCPs), if any.

Protocol field values in the "4***" to "7***" range are used for

protocols with low volume traffic which have no associated NCP.

Protocol field values in the "c***" to "f***" range identify

packets as link-layer Control Protocols (such as LCP).

Simpson [Page 4]

RFC 1661 Point-to-Point Protocol July 1994

Up-to-date values of the Protocol field are specified in the most

recent "Assigned Numbers" RFC [2]. This specification reserves

the following values:

Value (in hex) Protocol Name

0001 Padding Protocol

0003 to 001f reserved (transparency inefficient)

007d reserved (Control Escape)

00cf reserved (PPP NLPID)

00ff reserved (compression inefficient)

8001 to 801f unused

807d unused

80cf unused

80ff unused

c021 Link Control Protocol

c023 Password Authentication Protocol

c025 Link Quality Report

c223 Challenge Handshake Authentication Protocol

Developers of new protocols MUST obtain a number from the Internet

Assigned Numbers Authority (IANA), at IANA@isi.edu.

Information Field

The Information field is zero or more octets. The Information

field contains the datagram for the protocol specified in the

Protocol field.

The maximum length for the Information field, including Padding,

but not including the Protocol field, is termed the Maximum

Receive Unit (MRU), which defaults to 1500 octets. By

negotiation, consenting PPP implementations may use other values

for the MRU.


On transmission, the Information field MAY be padded with an

arbitrary number of octets up to the MRU.

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