Mario-
The GSS itself is meant to be an intelligent DNS server. What it provides:
1.) Probing for the answers it sends back to clients, dynamic removal of answers if probes fail.
2.) Failback clauses - if a primary set of answers are all unavailable, multiple other groups can be configured. This allows multiple levels of failure mitigation.
3.) Load based answering - using Kal-AP, the GSS can probe a CSS, CSM, or ACE device to determine which site is most/least loaded and send answers for a site accordingly.
4.) Proximity based answering. The GSS uses DRP agents to find which GSS is local to the client D-proxy and pull answers for that specific site.
5.) DOS attack prevention.
6.) CNR (full DNS server - a stand alone GSS only responds to A queries or forwards requests to an NS server.)
GSS Admin Guide
http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/gss4400series/v3.1.1/administration/guide/gssadmg.html
GSS Configuration Guide
http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/gss4400series/v3.1.1/configuration/cli/gslb/guide/cli_gslb.html
GSS - CNR Installation
http://www.cisco.com/en/US/docs/app_ntwk_services/data_center_app_services/gss4400series/v2.0/administration/guide/Man_CLI.html#wp1059313
CNR configurations
http://www.cisco.com/en/US/docs/net_mgmt/network_registrar/6.0/administration/guide/02GStart.html#wp1069420
http://cco.cisco.com/en/US/docs/net_mgmt/network_registrar/6.0/command/reference/cliref.html