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FIX Error SessionDisconnect: Session disconnected

What this error means

A session disconnect occurs when the FIX session is terminated unexpectedly. This can happen due to network issues, application errors, protocol violations, or explicit logout. When a session disconnects, messages may be lost, sequence numbers may become out of sync, and the session must be re-established with proper sequence recovery.

Common causes

  • Common causes include:

  • 1) Network connectivity issues (timeout, packet loss, connection reset),

  • 2) Protocol violation causing counterparty to disconnect,

  • 3) Application crash or restart,

  • 4) Heartbeat timeout (no messages received within HeartBtInt period),

  • 5) Explicit logout message (MsgType=

  • 5),

  • 6) Sequence number mismatch that cannot be recovered,

  • 7) Authentication failure or security violation.

Example log snippet

8=FIX.4.4|9=75|35=5|49=CLIENT|56=EXCHANGE|34=15|52=20231116-10:30:00|58=Session disconnected due to sequence gap|10=123|

How to fix it

1) Check network connectivity and firewall rules 2) Review logs for protocol violations or errors before disconnect 3) Implement proper heartbeat handling (send TestRequest if no messages received) 4) Ensure sequence numbers are persisted and recovered on restart 5) Send ResendRequest to recover missing messages after reconnection 6) Coordinate sequence reset if needed during logon 7) Verify authentication credentials are correct 8) Check for application errors or crashes in logs 9) Implement reconnection logic with exponential backoff

Related Knowledge Articles

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