LCP, described in RFC 1661, is a simple protocol to configure a common set of PPP connection parameters (for phase 1 of the PPP connection). It is also used by NCPs to configure specific data protocol configuration parameters (for phase 2 of the PPP connection). LCP uses the PPP Protocol ID 0xC0-21. Figure 4-1 shows an LCP frame.
Figure 4-1. The structure of an LCP frame
The fields in the LCP frame are defined as follows:
Code. A 1-byte field that identifies the type of LCP message
Identifier. A 1-byte field that identifies a specific pair of LCP messages: the request and the response
Length. A 2-byte length field that indicates ...