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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 Protocol Frame Formats

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PPP Link Control Protocol (LCP) Frame Formats
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12
3
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PPP Multilink Protocol (MP) Frame Format
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PPP Authentication Protocol (PAP, CHAP) Frame Formats
(Page 3 of 3)

PPP CHAP Control Frame Formats

The four CHAP frame types are formatted as shown in Table 40. As you can see in that table, the Challenge and Response frames use one message format, illustrated in Figure 39, while Success and Failure frames use a different one, shown in Figure 40.


Table 40: PPP Challenge Handshake Authentication Protocol (CHAP) Formats

Frame Type

Code Field

Identifier Field

Length Field

Data Field

Challenge

1

New value generated for each frame.

5 + Length of challenge text + Length of name

 

Response

2

Copied from the Identifier field of the Challenge frame for which this is a reply.

5 + Length of Value + Length of Name

Success

3

Copied from the Identifier field of the Response frame for which this is a reply.

4 (or more if extra data is included).

May contain an arbitrary, implementation-dependent Message field to indicate to the user whether authentication was successful or failed.

Failure

4



Figure 39: PPP CHAP Challenge and Response Frame Format

 



Figure 40: PPP CHAP Success and Failure Frame Format

 


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