How to act on unknown DefaultApplVerID on Logon message

1

What is the expected response when a Logon message with an unknown DefaultApplVerID is received?
Should a Logout be sent or the session just be disconnected?

I couldn’t find anything related on https://www.fixtrading.org/standards/fix-session-testcases-online/

The closest I could find is https://www.fixtrading.org/standards/fix-session-testcases-online/#scenario-2-receive-message-standard-header which talks about the BeginString in scenario “i”. Maybe I should be doing it similar for an unknown DefaultApplVerID?

Reference: https://github.com/quickfix-j/quickfixj/issues/681

2

DefaultApplVerID(1137) is about the application layer and hence similar to issues with the MsgType(35) value. These are covered by scenarios 2q and 2r, leading to a Reject(35=3) or BusinessMessageReject(35=j) message.

However, your issue is applicable to the Logon message, so that the session cannot really start as none of possible messages to follow can be accepted with this default application version. General issues with receiving the Logon message are covered by scenario 1Sd (Invalid Logon(35=A) message). This allows you to send a Reject(35=3) message to explain the reason before logging out and disconnecting.

1 Like
3

Scenario 1Sd looks good for my case, thank you.
I probably won’t send the optional Reject message because the session has not been established yet. Sounds strange to me to send messages to a session that has not already been established. But just my 2 cents. :slight_smile:

4

Sorry, follow-up question: what should I do when an app message with an unknown ApplVerID is received.
Should the message be rejected or simply be ignored (like a garbled message)? Is this similar to scenarios 2q and 2r that you mentioned @gtcpm ?
Thank you.