What public IP should I use for long-term network test?

What IP address is OK to ping -f for a prolonged time (the whole day)? "4.2.2.2" or something else?

The main concern is the admins there that may decide that it is some DoS and block/complain...

Maybe there is special dedicated public test server somewhere that sends ICMP replies (including fast enough), runs TCP and UDP echo servers and other tools?..

EDIT: **As pointed out by RedGrittyBrick and Hennes: ping -f is not a good idea on any public ip!

ping -t instead should imho not be a problem as this does not generate much network load.

I always use Google's DNS-Server-Adresses:

8.8.8.8

or

8.8.4.4

and never encountered any problems with packet-losts etc.

While I want to stress that leeching on someone else's service like this in a permanent setup is against my personal ethics, I will supply this pointer.

ICMP is often filtered or limited in rate of requests per source address, but HTTP services generally are not. You could use nping from nmap which (by default) uses TCP handshakes on port 80 rather than ICMP echoes to detect connectivity. As a bonus it works without being root on UNIX systems. The man page describes many, many options for it.

You'll have to either find a static address to a web server with good uptime (I have no idea how to tell if Google changes their front-end addresses) or rely on both a dns server AND a webserver. That might be an issue for your setup.