What is RDNSS Recursive DNS Server

The technical details of RDNSS (Recursive DNS Server).

1. Purpose:
   • RDNSS is an option in IPv6 Router Advertisements (RAs) that allows routers to inform IPv6 hosts about available DNS Recursive Server Addresses (DNS resolvers) and a DNS Search List.
   • It simplifies DNS configuration for hosts by providing them with DNS server information during network autoconfiguration.
2. How It Works:
   • When an IPv6 host joins a network, it listens for RAs from routers.
   • If an RA contains the RDNSS option, the host extracts the DNS server addresses and the search list.
   • The host then configures its DNS resolver settings based on this information.
3. RDNSS Option:
   • The RDNSS option includes the following details:
     • Addresses of DNS Recursive Servers: These are the IP addresses of DNS servers that can perform recursive DNS resolution.
     • DNS Search List: A list of domain suffixes (search domains) that the host appends to unqualified domain names before querying the DNS servers.
4. Benefits:
   • Stateless Configuration: RDNSS operates via stateless autoconfiguration, which means hosts can configure DNS settings without relying on DHCP.
   • Reduced Latency: By providing DNS server addresses directly, RDNSS reduces the time hosts spend searching for DNS servers.
   • Improved Network Efficiency: Hosts can promptly resolve domain names, enhancing overall network performance.
5. Example:
   • Suppose an IPv6 router sends an RA with the RDNSS option containing the addresses 2001:db8:1::1 and 2001:db8:2::2 as DNS servers and the search domain example.com.
   • An IPv6 host on the network will configure its DNS resolver to use these servers and append example.com to unqualified domain names.