How do I find my network IP address, netmask, and gateway info?

I have this command as an alias for "ipconfig" (up to 14.04):

nmcli dev list iface eth0 | grep IP4

An example listing is:

IP4-SETTINGS.ADDRESS:                   192.168.1.110
IP4-SETTINGS.PREFIX:                    24 (255.255.255.0)
IP4-SETTINGS.GATEWAY:                   192.168.1.1
IP4-DNS1.DNS:                           208.67.222.222
IP4-DNS2.DNS:                           208.67.220.220

If eth0 doesn't work, you may need to use eth1, eth2, ... depending on your configuration.

EDIT: 2/8/16

Note that this only works in versions before v15.04 (or possibly before v14.10; I have v14.04). For newer versions, you can use this:

 nmcli dev show eth0

You can use ifconfig, it will show your inet address (IP) and mask.

For the gateway, issue the ip route command and take note of the default route.

Hope this can help you.

This website explains how the network and broadcast addresses can be calculated via a netmask and a computer's ip address. To simplify that article: network is the lowest possible address in the range of ip addresses left over from the netmask. broadcast is the highest numbered ip address in that range. The "range of ip addresses left over from the netmask" is known as the local network.

"The network" typically means everyone above you, including the Internet. To get to "the network", the network address is used. In reality, most people call "the network" anything with ethernet cables that can talk to each other.

Example: your ISP gives you info to type into a wireless router: a static IP address of 99.1.81.209 and your netmask is 255.255.255.224. Now you're wanting to set up an ubuntu firewall and need to set up your public interface:

Calculate network IP address:
255.255.255.224 -> last octet = E0
 99.  1. 81.209 -> last octet = D1
Logical AND the mask and your ip: 
E0 & D1 = C0 = 192
--> network = 99.1.81.192

Calculate broadcast address:
255.255.255.224 : E0 -> there are 1F = 31,
-> broadcast = 99.1.81.192 + .31 = 99.1.81.223

The other way...

Calculate broadcast address:
255.255.255.224 -> last octet = E0
 99.  1. 81.209 -> last octet = D1
Hosts' IPs = 1F 
Logical OR the hosts ips with your ip:
1F | D6 = DF = 223 
--> broadcast = 99.1.81.223

Often, you'll see networks described with a /. Here's this network:

255.255.255.224 is the netmask, add up the "1" bits:
 8 + 8 + 8 + 3  = 27
so "this network" gets /27 notation
and can be described as 99.1.81.192/27