This solution applies to the Barracuda Backup Server, all firmware versions.
The Barracuda Backup Server establishes connection with the Barracuda Cloud Service over several ports. The same port access is necessary using the site to site deployment. Outbound access on these ports may need to be configured on the corporate firewall.
Ports 443 and 80 - the backup server sends periodic status updates to Barracuda Central over these ports.
Port 1194 - the Backup Server establishes a VPN connection to the Barracuda Cloud Service over this port. The Backup Server will appear offline if a firewall is blocking outbound access on port 1194, and cannot be configured properly without this connection.
Ports 5120-5129 - the Backup Server transmits binary data over these ports.
In some cases, restricting port access may not prevent the Barracuda Backup Service from functioning, but will prevent it from functioning optimally.
Note: These ports cannot be proxied through any edge device, unless exempted from the proxy or NAT'ed through a firewall. For more information, see this solution.
For information on used IP address ranges, see this solution.