If the Value received in a Response is equal to the expected value, then the implementation MUST transmit a CHAP packet with the Code field set to 3 (Success).
If the Value received in a Response is not equal to the expected value, then the implementation MUST transmit a CHAP packet with the Code field set to 4 (Failure), and SHOULD take action to terminate the link.
A summary of the Success and Failure 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ...
+-+-+-+-+-+-+-+-+-+-+-+-+-
3 for Success;
4 for Failure.
The Identifier field is one octet and aids in matching requests and replies. The Identifier field MUST be copied from the Identifier field of the Response which caused this reply.
The Message field is zero or more octets, and its contents are implementation dependent. It is intended to be human readable, and MUST NOT affect operation of the protocol. It is recommended that the message contain displayable ASCII characters 32 through 126 decimal. Mechanisms for extension to other character sets are the topic of future research. The size is determined from the Length field.