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In the config files of most applications, i.e. Apache 2.x, the solution is to put the square brackets around the IPv6 address, like this counterpart to above's IPv4 example: [::1]:80

Applications diverting from common syntaxes

TCPWrapper

In TCPWrapper's files /etc/hosts.allow and /etc/hosts.deny requires square brackets around the IPv6 network despite '/' would be a clear separator.

Example: [2001:1234:4321:abcd::]/64