To summarize: if only one host at a time needs an IP address, then 0.0.0.0/32 is used. If MANY hosts at a time need ip addresses, then 0.0.0.0/8 is used to DISTINCT them? The difference lies inside the address family: 0.0.0.0:22 : This is a listen socket which accepts connections on any interface, port 22 for IPv4 connections only. [::]:22 : Same here, but for IPv6 connections. LISTEN 0 128 *:80 *:* And this is a listen sockets which accepts IPv4 as well as IPv6 connection requests. The pts/0 is telling you which pseudo terminal the user is logged in on. In this case it's terminal 0. The (:0.0) tells you which hostname and display you're using. who am i is an alias of command who -m. See the man page for who. You can also read about the who command here. The output can definitely be confusing to a Unix novice. examples shows -m is same as am i [root@grinch]$ who am. The IP address 0.0.0.0 can have very different meanings, depending on where it's used. It's not a valid address to be given to an actual network interface, along with any other address in the 0.0.0.0/8 subnet (i.e. any address starting with 0.). It can't be used as the source address on any IP packet, unless this happens when a computer still doesn't know its own IP address and it's trying to. See here if you're confused about the differences b/w Bash's trap command and 0 vs. a signal 0 from kill: What is signal 0 in a trap command? Those two rules, together span the whole of 0.0.0.0/0 (the first one IP addresses from 0.0.0.0 to 127.255.255.255 and the second IP address from 128.0.0.0 to 255.255.255.255) and have precedence over the: default via 172.31.4.1 dev ens160 proto dhcp src 172.31.4.225 metric 100 rule (default being 0.0.0.0/0) as they have a narrower scope. Those are added by openvpn at least when you use. When setting up access control lists, what's the difference between 0.0.0.0/0 and ::/0? I'm seeing this for an AWS EC2 instance I'm setting up With DNS, what does 0.0.0.0 stand for? I have it set (Network and sharing settings → change adapter settings → Wireless network connection → Internet protocol v4 → Use the foll. I recently installed nginx and PHP-FPM via MacPorts on OS X 10.9 Mavericks and although it works my main error_log continuously says port 80 is in use. 2013/10/25 11:27:36 [emerg] 4510 0: bind() t. What's the difference in telling a service to run on localhost:xxxx, 127.0.0.1:xxxx and 0.0.0.0:xxxx? I needed to use 0.0.0.0 to get another host to be able to connect to my service.