What is ipv4.cat?
ipv4.cat is a server that simply replies with a remote address on all TCP ports.
How is this useful?
This provides a way of determining your public IP address from command line with the least amount of typing possible, without requiring the installation of any software. Similar to portquiz.net, it also provides a way of checking for outbound firewall blocks. ipv4.cat differs from services like ifconfig.me in that it returns a raw TCP response and therefore doesn't require a HTTP client.
ftp is recommended, as it is short, the most universal method across operating systems and is included in Windows by default (unlike