Reports the secondary (backup) DNS server address handed to a subscriber logging into this service. This is the fallback resolver a subscriber's device falls back to if the primary one defined by cssgServiceDNSPrimary doesn't answer, so a wrong or unreachable value here means DNS resolution for that service silently gets slower or fails entirely whenever the primary has a blip. A service provider running two DNS resolvers for redundancy would set cssgServiceDNSSecondary to a working backup resolver so a single primary-resolver restart doesn't take down name resolution for every subscriber on that service.