I was at a customer trying to connect a queue manager on z/OS down to distributed for the first time, and we were getting the message
CSQX202E MQPH CSQXRCTL Connection or remote listener unavailable, channel ... connection ...
TRPTYPE=TCP RC=00000468 (ECONNREFUSED) reason=00000000
This turned out to be a fire wall problem,
The TSO NETSTAT HOME command gave data like
10:1:2:15 LINKA P
Where the P indicates this is the primary interface.
The firewall had been to configured to only allow traffic from 10.1.2.16 down to the distributed machine. We were unable to start or ping the channel getting message CSQX202E return code 468.
Once the firewall was configued to have all of the host IP addresses, (10.1.2.15, 10.1.2.16 and 10.1.2.17) we could start the channel with no problems.
This was on the customer's production system, so we were not allowed to issue normal TCP PING commands, or TRACERTE etc.