We can't give you specific IP addresses as they are randomly assigned and can change at any time.. The common practice is to to allow connections from domains (ie *.codio.com, *.codio.io etc etc) and that covers everything you should ever need for proper running of all projects/guides etc).
See Firewall and Network Settings for more on this
If for any reason though, your firewall can only handle IP addresses, our services are hosted at Amazon and at the moment we are using us-east-1 zone.
The details of the ranges of IP addresses used in this zone can be found here: https://docs.aws.amazon.com/general/latest/gr/aws-ip-ranges.html