recursive lookups. This is useful for load balancing and service protection. Secondary Mode (or Slave Mode) Authoritative servers can publish content that originates from primary data storage (such as zone files or databases connected to business administration processes)--sometimes also called 'master' servers--or can be secondary (or slave) servers, republishing content fetched from and synchronized with such primary servers. Servers with a "secondary mode" feature have a built-in capability to retrieve and republish content from other servers. This is typically, though not always, provided using the AXFR DNS protocol. Caching Servers with this feature provide recursive services for applications, and cache the results so that future requests for the same name can be answered quickly, without a full DNS lookup. This is an important performance feature, as it significantly reduces the latency of DNS requests. DNSSEC Servers with this feature implement some variant of the DNSSEC protocols. They may publish names with resource record signatures (providing a "secure authority service"), and may validate those signatures during recursive lookups (providing a "secure resolver"). DNSSEC is becoming more widespread as the deployment of a DNSSEC root key has been done by ICANN. Deployment to individual sites is growing as top level domains start to deploy DNSSEC too. The presence of DNSSEC features is a notable characteristic of a DNS server. TSIG Servers with this feature typically provide DNSSEC services. In addition, they support the TSIG (Transaction SIGnature) protocol, which allows DNS clients to establish a secure session with the server to publish Dynamic DNS records or to request secure DNS lookups without incurring the cost and complexity of full DNSSEC support. IPv6 Servers with this feature are capable of publishing or handling DNS records that refer to IPv6 addresses. In addition to be fully IPv6 capable they must implement IPv6 transport protocol for queries and zone transfers in secondary/primary relationships and forwarder functions. Wildcard Servers with this feature can publish information for wildcard records, which provide data about DNS names in DNS zones that are not specifically listed in the zone. Split horizon Servers with the split-horizon DNS feature can give different answers depending on the source IP address of the query. Feature matrix Platforms In this overview of operating system support for the discussed DNS server, the following terms indicate the level of support: No indicates that it does not exist or was never released. Partial indicates that while it works, the