Support For IPv6 And For Mixed IPv6 And IPv4 Groups From MySQL 8.0.14, Group Replication group members can use IPv6 addresses as an alternative to IPv4 addresses for communications within the group. To use IPv6 addresses, the operating system on the server host and the MySQL Server instance must both be configured to support IPv6. For instructions to set up IPv6 support for a server instance, see Section 5.1.13, “IPv6 Support” . IPv6 addresses, or host names that resolve to them, can be specified as the network address that the member provides in the  group_replication_local_address  option for connections from other members. When specified with a port number, an IPv6 address must be specified in square brackets, for example: The network address or host name specified in  group_replication_local_address  is used by Group Replication as the unique identifier for a group member within the replication group. If a host name specified as the Group Replication local address for a server instance resolves to both an IPv4 and an IPv6 address, the IPv4 address is always used for Group Replication connections. The address or host name specified as the Group Replication local address is not the same as the MySQL server SQL protocol host and port, and is not specified in the  bind_address  system variable for the server instance. For the purpose of IP address permissions for Group Replication (see Section 18.6.1, “Group Replication IP Address Permissions” ), the address that you specify for each group member in  group_replication_local_address  must be added to the list for the group_replication_ip_allowlist  (from MySQL 8.0.22) or  group_replication_ip_whitelist system variable on the other servers in the replication group. A replication group can contain a combination of members that present an IPv6 address as their Group Replication local address, and members that present an IPv4 address. When a server joins such a mixed group, it must make the initial contact with the seed member using the protocol that the seed member advertises in the  group_replication_group_seeds  option, whether that is IPv4 or IPv6. If any of the seed members for the group are listed in the  group_replication_group_seeds  option with an IPv6 address when a joining member has an IPv4 Group Replication local address, or the reverse, you must also set up and permit an alternative address for the joining member for the required protocol (or a host name that resolves to an address for that protocol). If a joining member does not have a permitted address for the appropriate protocol, its connection attempt is refused. The alternative address or host name only needs to be added to the  group_replication_ip_allowlist  (from MySQL 8.0.22) or group_replication_ip_whitelist  system variable on the other servers in the replication group, not to the  group_replication_local_address  value for the joining member (which can only contain a single address). For example, server A is a seed member for a group, and has the following configuration settings for Group Replication, so that it is advertising an IPv6 address in the  group_replication_group_seeds  option: Server B is a joining member for the group, and has the following configuration settings for Group Replication, so that it has an IPv4 Group Replication local address: Server B also has an alternative IPv6 address  2001:db8:8b0:40:3d9c:cc43:e006:19e8 . For Server B to join the group successfully, both its IPv4 Group Replication local address, and its alternative IPv6 address, must be listed in Server A’s allowlist, as in the following example: 3757 group_replication_bootstrap_group=off group_replication_local_address= "203.0.113.21:33061" group_replication_group_seeds= "[2001:db8:85a3:8d3:1319:8a2e:370:7348]:33061" group_replication_bootstrap_group=on group_replication_local_address= "[2001:db8:85a3:8d3:1319:8a2e:370:7348]:33061" group_replication_group_seeds= "[2001:db8:85a3:8d3:1319:8a2e:370:7348]:33061" group_replication_local_address= "[2001:db8:85a3:8d3:1319:8a2e:370:7348]:33061"