What occurs when a datagram is sent to a 127.x.y.z address?

When a datagram is sent to a 127.x.y.z address, it is specifically directed to the loopback interface of the host. This means that the datagram does not leave the host system; instead, it is processed as if it had been sent from the host to itself.

The significance of the loopback address is that it allows for testing and communication within the same device without needing to engage with the physical network. Applications can connect to services running on the same machine using this address, which is helpful for various development and diagnostic purposes.

In this context, the other options do not apply since the datagram is not discarded, it does not exit through the network interface card, and it is not forwarded to another host but instead remains confined to the original host. The behavior involving the 127.x.y.z address is an essential aspect of network design and is widely utilized in troubleshooting and software development.