IPv6 Router Advertisement Options for DNS Configuration (RFC6106)

Publication date  : November 2010
RFC Author(s)       : S. Park, L. Beloeil, S. Madanapalli
Category              : Standards Track

This article describe some specifications of RA DNS options, which allow  to IPv6 routers to advertise a list of DNS recursive server addresses and a list of Domain name server Search List to an IPv6 node.

RA Options are based on Neighbor Discovery (ND) for IPv6 stateless  autoconfiguration, that provide a simple way to configure mobile node in a IPv6 network and which make ability to nomadic hosts to reach Internet Services. In this document (section 5) the IPv6 DNS configuration defines two ND  options :

1. The Recursive DNS Server (RDNSS) Contains one or more IPv6 addresses of recursive DNS servers, this Option Format contain 4 field :
Type (8-bit), Length (8-bit), Reserved(16-bit), Lifetime(32-bit) and Addresse of IPv6 Recursive DNS servers (128-bit)

2. The DNS Search List (DNSSL) Contains one or more domains name, this Option Format contain 4 field :
Type (8-bit), Length (8-bit), Reserved(16-bit), Lifetime(32-bit) and Domain Names of DNS Search List (128-bit)

Section 5.1, define that a packet with lifetime value set all one bits (0xffffffff) represents infinity, which mean that the node must keep the DNS parameters, until next update.

Section 5.2, define that a packet with lifetime value set to zero means that RDNSS address must no longer be used.

The RFC describe also, that storing RDNSS addresses from at least two different sources is highly recommended.

Source : https://tools.ietf.org/html/rfc6106

IPv6 Router Advertisement Options for DNS Configuration (RFC6106)

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