If some Configuration Options received in a Configure-Request are not recognizable or are not acceptable for negotiation (as configured by a network administrator), then the implementation MUST transmit a Configure-Reject. The Options field is filled with only the unacceptable Configuration Options from the Configure-Request. All recognizable and negotiable Configuration Options are filtered out of the Configure-Reject, but otherwise the Configuration Options MUST NOT be reordered or modified in any way.
On reception of a Configure-Reject, the Identifier field MUST match that of the last transmitted Configure-Request. Additionally, the Configuration Options in a Configure-Reject MUST be a proper subset of those in the last transmitted Configure- Request. Invalid packets are silently discarded.
Reception of a valid Configure-Reject indicates that when a new Configure-Request is sent, it MUST NOT include any of the Configuration Options listed in the Configure-Reject.
A summary of the Configure-Reject 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 ... +-+-+-+-+
4 for Configure-Reject.
The Identifier field is a copy of the Identifier field of the Configure-Request which caused this Configure-Reject.
The Options field is variable in length, and contains the list of zero or more Configuration Options that the sender is rejecting. All Configuration Options are always rejected simultaneously.