Internet Protocol Control Protocol (IPCP) Frames

The Internet Protocol Control Protocol (IPCP) is used to configure, enable, and disable IP over PPP links. It uses the same frame exchange mechanism as the link control protocol (LCP).

IPCP frames have the general form shown in Figure A-8.

Figure A-8 IPCP Frame Format

Address Field

The address field is one octet in length, and is part of the HDLC-like framing for PPP. It is always set to 0xff.

Control Field

The control field is one octet in length, and is part of the HDLC-like framing for PPP. It is always set to 0x03.

Protocol Id

The protocol id identifies the type of information contained in the information field of the frame, and is always 0x8021 for IPCP frames.

Code Field

The code field is one octet in length and identifies the type of IPCP frame, based on the following codes:

0x01 Configure-request 0x05 Terminate-request

0x02 Configure-ack 0x06 Terminate-ack

0x03 Configure-nak 0x07 Code-reject

0x04 Configure-reject

Id Field

The id field is one octet in length, and carries an identifier that is used to match associated requests and replies.

Length Field

The length field is two octets in length, and indicates the total length of the IPCP frame including the code, id, length, and data fields. The length must not exceed the maximum receive unit (MRU).

Data Field

The data field is zero or more octets in length, as indicated by the length field. It contains the information associated with the frame, which may be configuration options, frame information, or simple data, in a format determined by the code field.