What is the difference between 0.0.0.0 and 127.0.0.1 ?

network-connectivity

These two IP addresses have different uses and meanings in the context of networking.

Loopback 127.0.0.1

127.0.0.1 is known as the loopback address. This IP address is used to establish a network connection to the same device, usually used for testing. It’s basically your own computer’s way of referring to itself without needing to know its IP address in a larger network or on the internet. In other words, if a program in your computer sends a network request to 127.0.0.1, it will be looped back to the same machine. All IPv4 networks reserve 127.0.0.0 to 127.255.255.255 for loopback purposes, but 127.0.0.1 is the most commonly used.

All Local IPv4: 0.0.0.0

0.0.0.0 has a couple of different meanings, but it’s generally a non-routable meta-address used to designate an invalid, unknown, or non-applicable target (a “no particular address” place holder). In the context of servers, 0.0.0.0 means “all IPv4 addresses on the local machine”. If a host has two IP addresses, 192.168.1.1 and 10.1.2.1, and a server running on the host listens on 0.0.0.0, it will be reachable at both of those IP addresses.

Conclusion

127.0.0.1 is used to establish a network connection to oneself, and is typically used for testing.

0.0.0.0 is used to refer to all IP addresses on the local machine. If a server is set to listen to 0.0.0.0, it will be listening to all of the IP addresses the machine has.

In the container (k8s kubernetes, docker), you might want to listen to port 0.0.0.0 intead of 127.0.0.1 which may not work.

–EOF (The Ultimate Computing & Technology Blog) —