An implementation wishing to open a connection MUST transmit a Configure-Request. The Options field is filled with any desired changes to the link defaults. Configuration Options SHOULD NOT be included with default values.
Upon reception of a Configure-Request, an appropriate reply MUST be transmitted.
A summary of the Configure-Request packet format is shown below. The fields are transmitted from left to right.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+
1 for Configure-Request.
The Identifier field MUST be changed whenever the contents of the Options field changes, and whenever a valid reply has been received for a previous request. For retransmissions, the Identifier MAY remain unchanged.
The options field is variable in length, and contains the list of zero or more Configuration Options that the sender desires to negotiate. All Configuration Options are always negotiated simultaneously. The format of Configuration Options is further described in a later chapter.