Domino supports both IPv6 and IPv4. Thus, if an IPv6-enabled Domino server encounters an IP address in IPv4 format, the Domino server can still make the connection to that address.
In DNS, records that store IPv6 addresses are called AAAA records. After you enable IPv6 on a Domino server and add the server's AAAA record to DNS, another IPv6-enabled Domino server can connect to it only over IPv6. Servers that don't support IPv6 can run Domino with IPv6 support disabled, which is the default. These servers can successfully connect to IPv6-enabled Domino servers only if the DNS for the IPv6 servers contain A records.
Using IPv6 in a Domino network
For best results when using IPv6 with Domino servers, set up network devices in the network pathway to connect directly with native IPv6, rather than tunnel through the IPv4 network.
How Lotus Domino decides whether to connect over IPv6 or IPv4
A Domino server evaluates the address format and then, based on that information, makes an IPv4 or an IPv6 connection.