Jim is correct, but I need to add one thing that has caused some people to get confused:
When you ping your DynDNS address, you land at your router. Often, the result of a ping will
be a timeout. This is because ICMP reply is often turned off by default for security reasons.
If you receive a timeout when you ping your router, you need to turn "ICMP packet reply" or
similar on. This is usually under the firewall or security settings.
73,
Mitch DJ0QN / K7DX