IPv6 and Domino®

You can enable IPv6 support in HCL Domino® for SMTP, POP3, IMAP, LDAP, and HTTP services on IBM® AIX®, IBM® i, and Linux systems.

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. When attempting to connect to a server, Domino® tries to resolve all IP addresses for a server until one works. This allows a server to have both an IPv4 address and an IPv6 address. Domino® caches the last successful address for a server and uses only the cached address to quickly search for a server. If you do not want to use only the cached address, enter the NOTES.INI setting DONT_USE_REMEMBERED_ADDRESSES=1.

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.

Enabling IPv6 on Notes® and Domino®

To enable IPv6 on Notes® and Domino®, add the setting TCP_ENABLEIPV6=1 to the NOTES.INI file on both the Notes® client and the Domino® server.

How 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.

Table 1. Address format and server response

Address format

Server response


Makes an IPv4 connection.

IPv4 address mapped to IPv6

Attempts to make an IPv6 connection and waits for the TCP/IP software to make either an IPv6 or IPv4 connection, depending on the remote system's TCP/IP stack.


Makes an IPv6 connection.

Server name

Uses DNS to resolve the name:

  • If only an A record is found, connects over IPv4.
  • If only an AAAA record is found, connects over IPv6 or waits for the TCP/IP software to make the connection.
  • If both an A record and AAAA record are found, uses the AAAA record.