You might encounter the following issues when preparing services for IPv6 support:
Certain applications, even after being ported to IPv6, do not turn on IPv6 support by default. You might have to configure these applications to turn on IPv6.
A server that runs multiple services, some of which are IPv4 only and others that are both IPv4 and IPv6, can experience problems. Some clients might need to use both types of services, which can lead to confusion on the server side.