How DNS Works
An overview of how DNS works and is implemented on the system.
Summary
The Domain Name System translates a host name or domain name to an IP address. The system allows you to configure Authoritative Domain Name Server (ADNS), DNS proxy server, End Resolver and Forwarder on the system. The system allows you to add DNS resource records such as SRV Records, AAAA Records, A Records, MX Records, NS Records, CNAME Records, PTR Records, and SOA Records. The system can also load-balance external DNS servers.
An ADNS provides the IP address of a requested domain and is essential in a GSLB setup. To configure the system as an ADNS, you must create a GSLB setup and then create an ADNS service.
After creating an ADNS service, you can make the system authoritative for a domain through domain delegation. Domain delegation is the process of adding two name server records to the authoritative name server that was previously responsible for providing the IP for a domain. These name server records indicate that the system is the authoritative server for a domain. When a client sends a DNS request for this domain, the domain name system queries the system to map the domain name to its IP address.
The system can also cache DNS responses and function as a DNS proxy. This enables the system to provide quick responses for repeated translations. To configure the system as a DNS proxy, you must enable caching of DNS records. You must also create a load balancing DNS vserver, create DNS services, and bind these services to the vserver. Cached data times out periodically. So, the system provides you the option to set the lifetime (TTL) of the cached data.
The system also allows caching of negative responses for a domain. This is called negative caching. Negative caching helps speed up responses to queries on a domain and optionally, the record type. If a negative response is present in the local cache, an error message for non-existent domain (NXDOMAIN error message) is returned to the client. If the response is absent in the local cache, the query gets forwarded to the backend server and the backend server returns an NXDOMAIN error to the system. The system then returns this error message back to the client after caching the response locally.
There are two ways in which DNS resolution occurs
- Recursive resolution
- Iterative resolution
In iterative resolution, the name server provides an intermediate name server that has the address of the ADNS for the domain.
In recursive resolution, the resolver (DNS client) sends a recursive query to a name server for a domain name. If the queried name server is authoritative for the domain, it responds with the requested domain name. Otherwise, it queries the name servers recursively till the requested domain name is found.
The system supports recursive query and you can configure this by enabling the recursive query option. You can also set the number of times the DNS resolver must send a resolution request (DNS retries), if a DNS lookup fails.
The system can be configured as a DNS forwarder. A forwarder passes DNS requests to external name servers. The system allows you to add external name servers and provides name resolution for domains outside the network. The system also allows you to set the name lookup priority to DNS or WINS.
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