The totd DNS proxy can treat each AAAA query in a special way. This behaviour is enabled when one or more prefixes are configured. Such a prefix is configured on the command line, in the totd config file, or dynamically using a web form if the optional small webserver is compiled in.

If the nameserver that totd forwards the AAAA query to, does not return an IPv6 address for the AAAA query, totd will make a second query but this time for an A record of the hostname of the original query. The resulting IPv4 address is then used to construct a fake IPv6 address, by replacing the lower 32 bits of the specified prefix with this IPv4 address. The resulting IPv6 address is sent as response to the original AAAA record query. In addition, totd treats PTR type queries (reverse name lookup) in the ip6.int. and ip6.arpa. domains specially. If the query matches a specified prefix, totd will forward a PTR query for an IPv4 address (using the lower 32 bits of the address to construct an IPv4 address) instead and use that to construct a faked response to the original PTR query.

If multiple prefixes are configured, totd will cycle through them in round robin fashion. In this way totd can balance the load for multiple NAPT-PT/TRT translators in a network and support to some extent redundancy in the setup of transitioning mechanisms in a network. The totd proxy has no way to check itself whether the prefixes it uses are actually ‘live’, i.e. can be used to contact remote (IPv4-only) machines. However, a separate monitoring tool or the transitioning mechanisms itself may have support for this. For this reason, the latest version of totd can be configured dynamically using a small built-in webserver. A totd proxy can listen on some TCP port for http requests that tell it do add or delete a prefix from its list of prefixes. A network administrator can then use a web browser to reconfigure a running totd, or (more likely) use tools to do so from automated scripts.