What range of ports should be open for Graphical Console of Cloudmin

Every time I want to connect to guest system through Graphical Console of Cloudmin, it gives:

Network error: could not connect to server:hosname:port-number

with port number changing constantly for every other guest system, and I have to open up that port separately in my servers firewall. What range of IPs I need to keep open in firewall not to do this every single time I want to get connected through the console? Thanks!