Exchange FIX API
4 (Sequence reset)
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4 (Sequence reset)

The 4 (Sequence Reset) typically refers to a sequence number reset in a FIX session.

This can happen for various reasons, such as recovering from a connectivity issue or ensuring synchronization between the two parties in the FIX communication.

TagNameTypeRequiredDescription
123GapFillFlagBooleannoIndicates that the 4 (Sequence Reset) message is replacing administrative or application messages which will not be re-sent.

Supported values:
  • Y (Gap Fill message, MsgSeqNum field valid).

    Gap Fill mode - the message is used in response to a 2 (Resend Request) when one or more messages must be skipped.
  • N (Sequence Reset, ignore MsgSeqNum).

    Reset mode - specifying an arbitrarily higher new sequence number to be expected by the receiver of the 4 (Sequence Reset) message, and is used to re-establish a FIX session after an unrecoverable application failure.
36NewSeqNoSeqNumyesNew sequence number.

For a sample message and other details, see FIX 4.4 : Sequence Reset <4> message in the FIX 4.4 documentation.

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