The sim uses only UDP traffic, so if the others using your Internet connection are using mostly TCP, and you can give priority to UDP traffic, that would be an easy first step.
There are two ends to each communication: the local end (your computer), and the server end (our server).
For the sim:
We use "ephemeral" ports on the local end. This means that your computer finds an unused port number, and uses it for its end of the connection. There is not much you will be able to do with that, since most programs do this same thing.
We use a fixed range of ports (15000..52500) on our race servers. Hopefully you can specify port ranges, and not just individual port numbers.
If you can give priority to (remote) IP address ranges, instead of port numbers, that would be more reliable.
Note: A server being listed below does not necessarily mean that it is up and running as servers may come in and out of maintenance.
US Farm
bosrace01-orig.iracing.com --> 208.118.226.161
bosrace02-orig.iracing.com --> 208.118.226.162
bosrace03-orig.iracing.com --> 208.118.226.163
bosrace04-orig.iracing.com --> 208.118.226.164
bosrace05-orig.iracing.com --> 208.118.226.176
bosrace06-orig.iracing.com --> 208.118.226.166
bosrace07-orig.iracing.com --> 208.118.226.177
bosrace08-orig.iracing.com --> 208.118.226.168
bosrace09-orig.iracing.com --> 208.118.226.169
bosrace10-orig.iracing.com --> 208.118.226.170
bosrace11-orig.iracing.com --> 208.118.226.171
bosrace12-orig.iracing.com --> 208.118.226.172
bosrace13-orig.iracing.com --> 208.118.226.173
bosrace14-orig.iracing.com --> 208.118.226.174
bosrace15-orig.iracing.com --> 208.118.226.175
Sydney Farm
sydrace01-orig.iracing.com --> 101.0.91.230 --> 2401:fc00:0:10c::8
sydrace02-orig.iracing.com -->101.0.103.46 --> 2401:fc00:0:10f::8
sydrace03-orig.iracing.com -->101.0.77.34 --> 2401:fc00:0:133::2
Amsterdam Farm
amstrace03-orig.iracing.com --> 83.149.102.49 --> 2001:1af8:4500:a028::1
amstrace04-orig.iracing.com --> 95.211.179.20 --> 2001:1af8:4500:a056::20:
amstrace05-orig.iracing.com --> 95.211.179.21 --> 2001:1af8:4500:a056::21:
amstrace06-orig.iracing.com --> 95.211.179.54 --> 2001:1af8:4500:a056::54: