In a typical GSLB deployment of the Barracuda Load Balancer, the existing DNS domain nameserver continues as the authoritative nameserver for the zone or domain, e.g. barracuda.com. But a hostname or sub-domain, e.g. www, is delegated to the Barracuda Load Balancer that acts as the GSLB Controller. When a DNS query for www.barracuda.com is received, it is forwarded to the GSLB Controller.
The GSLB Controller acts as the authoritative DNS server for delegated sub-domains, returning definitive answers to DNS queries about domain names installed in its configuration. On the GSLB Controller you can identify one or more IP addresses of sites that serve a single domain name. When asked to resolve a host, the GSLB Controller returns a list of IP addresses of the sites that are both available and that match the site selection algorithm.