Stateless Auto-configuration
Routing configuration and DNS

Address auto-configuration allows also determining the routing information. It uses the following fundamental data structures that can be implemented as a single entity using the routing table:

In the case of support for mobility, the Binding Cache is added. It indicates that the target node communicates at temporarily assigned address. It means that the Routing header will be added to the outgoing datagram and its destination address will be changed.

The procedure for sending a datagram is depicted in the following diagram.

The Procedure for Sending a Datagram

Redirect

Routers send Redirect message to inform a host of a better first-hop node on the path to a target node. Hosts can be redirected to a better first-hop router but can also be informed by a redirect message that the target node is in fact a neighbor. Redirect message contains the destination address of datagram and the address of router or target node itself, to which the datagrams are sent to the target node. This address is written in the Target Address field. It is also possible to include the link-layer address of the router and the datagram header that caused a redirection. This header must be limited in size not to exceed a total length of the message that must be smaller than 1280 octets.

Redirect Message Format

DNS configuration

The fundamental mechanisms of stateless address auto-configuration do not support the configuration of DNS server addresses, which is a disadvantage because the form of IPv6 addresses. Therefore, it was defined the RFC 6106 that adds two new options to the RA message for DNS:

For example, if Search List contains an entry cvut.cz, so it is possible to access www.cvut.cz website just typing www in a host. The first a host will try to find the IPv6 address for www in DNS server and if it fails, it will repeat the procedure with prefix according the list. So, it will find the IPv6 address for www.cvut.cz.

All of the addresses share the same lifetime value. If it is desirable to have different Lifetime values, multiple DNS options can be used. The recommended lifetime ranges from the maximum interval between two RA messages to double value of this interval. The zero value of lifetime has a special meanings, the corresponding DNS address is deleted from the IPv6 host.

When an IPv6 host receives RA message with DNS options, the validity of DNS options is checked. If the DNS options are valid, the host should copy, update or delete the values of the options into the DNS Repository and the Resolver Repository based on RA message content. Otherwise, the host must discard the options. The recommended number of DNS addresses is three. When the number of DNS addresses is already the sufficient number, the new one replaces the old one that will expire first in terms of lifetime.

In the case where the DNS options of RDNSS and DNSSL can be obtained from multiple sources, such as RA and DHCPv6, the IPv6 host should keep some DNS options from all sources.