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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

PPP General Frame Format 1 2 3 4 PPP Link Control Protocol (LCP) Frame Formats

PPP Control Message Option Format

The various Configure- messages are used to negotiate configuration options in LCP and the other control protocols. In their Data fields they carry one or more options that are, again, specific to the protocol using them. For example, LCP uses one set of configuration options for the link as a whole; CCP uses options to negotiate a compression algorithm, MP uses it to set up multilink bundles and so on. Figure 35 shows how these options, which can vary in length, are placed in the Data field of a PPP control message (which is in turn nested inside the general PPP frame format).

Again, there is commonality here; while every option is different, they all use the same basic format, as described in Table 37 and illustrated in Figure 36:

The configuration options are described briefly in the individual protocol topics. I am not showing the specific contents of each option as there are just too many of them. These are in the RFCs.

Figure 36: PPP Control Message Option Format

Each option that appears in any of the many PPP control message types consists of this triplet of Type, Length and Data.

PPP General Frame Format 1 2 3 4 PPP Link Control Protocol (LCP) Frame Formats

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