We use software from Genesys that uses its own proprietary protocols (all TCP) and we often run into issues with customers firewalls. The ports we are using are 2000, 2200 and 3010 - I'm not sure where we came up with these but thats what we do for every deployment.
The problem is we run into lots of issues even when the port has been opened on the firewall.. Some firewalls still give us grieve for the traffic and this usually comes down to the fact we have used a port that is well known and firewalls want to be fancy and make sure the traffic on that port matches the expected protocol/traffic. An example of this is port 2000 which is Cisco SCCP.
My question: is there any ports that would be best to use for proprietary protocols like this? For example, ports that don't have default firewall inspection behaviour.
It's very painful especially when the person operating the firewall doesn't really understand it well - sometimes it takes them a long time to realise it's doing this type of inspection/blocking since they've added a rule to allow it..
[UPDATE 2020-04-01] I've updated the post to hopefully make it a bit clearer. I understand that the ports need to be opened on the firewall - my question and the issues I've experienced is around the firewall still inspecting/blocking/impacting traffic even after the port has been allowed.