In most home networks, you have a router connected to your ISP modem so that more than one computer can be connected at the same time.
The router is often built-in with the modem, so it may not be very obvious.
To see if you are assigned your external ip or are behind a router, follow these instructions:
1. Hit Win-R, type 'cmd' and hit enter (or Start > Run > All programs > Accessories > Command prompt)
2. Type ipconfig
3. Check the field 'IPv4 Address'
Your external address is 18.104.22.168, if these are identical then you are not behind a router.
If the address starts with 192.168. then this is an internal IP address.