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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 Feature Protocols

PPP Compression Control Protocol (CCP) and Compression Algorithms 1 2 3 4 PPP Multilink Protocol (MP/MLP/MLPPP)

ECP Configuration Options and Encryption Algorithms

ECP configuration options are used only to negotiate the type of encryption algorithm to be used by the two devices, and the specifics of how that algorithm is to be employed. The device initiating the negotiation sends a Configure-Request with one option for each of the encryption algorithms it supports. The other device compares this list of options to the algorithms it understands. It also checks for any details relevant to the option to see if it agrees on how that algorithm should be used. It then sends back the appropriate reply (Ack, Nak or Reject) and a negotiation ensues until the two devices come up with a common algorithm both understands. If so, encryption is enabled, and otherwise, it is left turned off.

The ECP configuration options begin with a Type value that indicates the encryption algorithm. When the Type value is 0, this indicates that the option contains information about a special, proprietary encryption method not covered by any RFC standards, which can be used if both devices understand it. Values in the range from 1 to 254 indicate encryption algorithms that have been defined for use with ECP; at present, only two are defined. Table 31 shows the values of the Type field, including the encryption algorithm each corresponds to and the number of the RFC that defines it:

PPP Compression Control Protocol (CCP) and Compression Algorithms 1 2 3 4 PPP Multilink Protocol (MP/MLP/MLPPP)