All Gearset requests originate from one of four static IP addresses:
52.30.99.11434.246.69.14834.246.80.17052.208.77.76
Depending on your corporate firewall settings, you may need to whitelist logins from these IPs for Gearset to be able to connect to your on-premise version control system or to orgs with IP access restrictions enabled.
You should allow TCP port 443 for HTTPS (or TCP port 22 for SSH).