Solaris DNS Reference : Types of DNS Servers
1. Root Servers:
Root servers are positioned at the top or root of the DNS hierarchy, and maintain data about each of the top-level zones. The root servers are maintained by the NIC and have been moved to a common domain for consistent naming purposes. The root servers are named as A.root-servers.net., B.root-servers.net., and so on.
This file is obtained from : ftp://ftp.rs.internic.net/domain/named.root
2. Primary(Master) Servers:
Each domain must have a primary server. Primary server has the following features.
- There is generally only one primary server per domain.
- They are the system where all the changes are made to the domain.
- They are the authoritative for all domains they serve.
- They periodically update and synchronize secondary servers of the domain.
- In BIND 8.1.2, they are defined by the type master argument to the zone statement in the configuration file /etc/named.conf.
3. Secondary servers:
Each domain should have at least one secondary server. In fact,the NIC will not allow a domain to become officially registered as a subdomain of a top-level domain until a site demonstrates two working DNS servers. Secondary servers have the following features.
- There is one or more secondary server per domain.
- They obtain copy of the domain information for all domains they serve from the appropriate primary server or another secondary server for the domain.
- They are authoritative for all the domains they serve.
- They periodically receive updates from the primary servers of the domain.
- They provide load sharing with the primary servers and other servers of the domain.
- They provide redundancy in case one or more other servers are temporarily unavailable.
- They provide more local access to name resolution if placed appropriately.
- In BIND 8.1.2, they are defined by the type slave argument to the zone statement in the /etc/named.conf file.
4. Caching-Only servers
These servers only cache information for any DNS domain. They are not authoritative for any domain. Caching-only servers provide the following features.
- They provide local cache of looked up names.
- They have lower administrative overhead.
- They are never authoritative for any domain
- They reduce overhead associated with secondary servers performing zone transfers from primary servers.
- They allow DNS client access to local cached naming information without the expense of setting up a DNS primary or secondary server.
5. Forwarding servers:
Forwarding servers are a variation on a primary or secondary server and act as focal points for all off-site DNS queries. Designating a server as a forwarding server causes all off-site requests to go through that server first. Forwarding servers have the following features.
- They are used to centralize off-site requests
- The server being used as a forwarder builds up a rich cache of information.
- All off-site queries go through forwarders first.
- They reduce the number of redundant off-site requests
- No special setup on forwarders is required
- If forwarders fail to respond to queries, the local server can still contact a remote site, DNS servers itself.