If the internet connection isn't working, Android doesn't provide you much tools for troubleshooting. This App however instantly informs you, if you got an IP address and if the DNS server is reachable.
The special thing about this network analyzer tool is, that it supports IPv6 as well!

The main features are:
- Display of current IP address (includes the public address)
- Display of gateway and DNS server
- Probes both the gateway and the DNS servers for reachability
- List of all network interfaces of this device
- IPv6 support

One thing about the usage: Long tap on an icon to get a description of its meaning.

Depending on the device and the version of Android, some features may not be available.