[binwiederhier]

Well, this was a surprise to me too, but apparently Linux does this:

   $ ping 0.0.0.0
   PING 0.0.0.0 (127.0.0.1) 56(84) bytes of data.
   64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.028 ms
   64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.056 ms
   64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.105 ms
   ...

   $ nc 0.0.0.0 22  
   SSH-2.0-OpenSSH_8.9p1 Ubuntu-3ubuntu0.10
   ...

[focusedone]

ping 0 works too. Kinda fun.

[mh0pe]

Fun fact, ping 0 works because 0 is the IP decimal notation of 0.0.0.0. One of my favorite age-old WAF bypass since it doesn't match octet notation regexes that are often in place.