The first place to look when diagnosing connectivity problems is the IAF log. Each FIX session should produce the following series of messages upon successfully connecting and logging on to the remote system:

If after attempting to connect you do not see “Initiated logon request”, it is likely that a connection to the specified host/port cannot even be established. In this instance you must investigate your environment/network and establish that a route to the target system is actually possible.

If you do see “Initiated logon request” but no response is received or the connection is terminated by the peer in some way then it is likely that the target system has rejected the logon attempt. In this case you need to look at the FIX message log and investigate the message exchange. It may be that you have provided incorrect details or some essential tag is missing from the logon message.

Another possibility in this instance is that there is a sequence number mismatch. The target system will report this to you and tell you what it expects the sequence number to be. In this case you must shutdown the adapter, edit the sequence number file (discussed above) and make sure that the sequence numbers are correctly aligned with what you and the target system are expecting before restarting.

Once a FIX session is properly established and as long as the sessions have been properly configured by sending in the relevant SessionConfiguration event(s) (See FIX Client Monitors, the session manager will notify all the other FIX service monitors that the session(s) are now up. This will also be logged in the service log as:

…

The first message tells us that the session manager is receiving heartbeats from the IAF and the second message tells us that the session manager has received a logon message for that connection.