pre login initialization =29237; handshake=26244 Connecting to one of my servers (no mirror or availability group running), from a local machine and I get this error message below related to handshake when the firewall is up.

when the firewall is down it connects straight away.

the question I would like to address is:

is it always these number below (29237 and 26244) that sql server uses for connection?

I am aware of the port numbers on single and multiple instances.

This server by the way is not a named instances.

initialization =29237; handshake=26244

or does it change? if so then - based on what?

we have had issues with one domain controller but I have ruled that out. 



I haven't even touched authentication schemas and Kerberos
By default, SQL uses port 1433 and 1434 (if you are using named instance or the DAC connection). 

You can validate which port is used using SQL Server Configuration Manager