On some IPv4-only networks, DNS results sometimes include AAAA records. Most programs correctly handle this situation and fall back to the A record. For example, if you curl `www.torproject.org`, it uses the A or AAAA record depending on whether you are on a IPv6 or IPv4 network: anarcat@curie:~(main)$ curl -s -v -I www.torproject.org 2>&1 | head -1 * Trying 116.202.120.165:80... anarcat@marcos:~$ curl -s -v -I www.torproject.org 2>&1 | head -1 * Trying 2604:8800:5000:82:466:38ff:fecb:d46e:80... marcos is on an IPv6 network, curie isn't. Web browsers also handle this gracefully. oping (and, obviously noping) doesn't handle this correctly: anarcat@curie:~(main)$ oping -c 1 www.torproject.org PING www.torproject.org (2a01:4f8:fff0:4f:266:37ff:feae:3bbc) 56 bytes of data. echo reply from www.torproject.org (2a01:4f8:fff0:4f:266:37ff:feae:3bbc): icmp_seq=1 timeout --- www.torproject.org ping statistics --- 1 packets transmitted, 0 received, 100,00% packet loss, time 0,0ms For what it's worth, iputils-ping doesn't have the same bug, but that's only because it defaults to IPv4 instead, which isn't ideal: anarcat@marcos:~$ ping -c 1 www.torproject.org PING www.torproject.org (38.229.82.25): 56 data bytes 64 bytes from 38.229.82.25: icmp_seq=0 ttl=57 time=29,997 ms --- www.torproject.org ping statistics --- 1 packets transmitted, 1 packets received, 0% packet loss round-trip min/avg/max/stddev = 29,997/29,997/29,997/0,000 ms anarcat@curie:~(main)$ ping -c 1 www.torproject.org PING www.torproject.org (95.216.163.36) 56(84) bytes of data. 64 bytes from hetzner-hel1-03.torproject.org (95.216.163.36): icmp_seq=1 ttl=44 time=129 ms--- www.torproject.org ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 128.706/128.706/128.706/0.000 ms ... but that's a different question. the `oping` manpage specifically advertises IPv6 support this way: In contrast to the fping utility (URL is listed in "SEE ALSO") oping can use both, IPv4 and IPv6 transparently and side by side. And, for what *that's* worth, fping actually does the correct thing here: anarcat@marcos:~$ fping -A -c 1 www.torproject.org 2604:8800:5000:82:466:38ff:fecb:d46e : [0], 64 bytes, 34.9 ms (34.9 avg, 0% loss) 2604:8800:5000:82:466:38ff:fecb:d46e : xmt/rcv/%loss = 1/1/0%, min/avg/max = 34.9/34.9/34.9 anarcat@curie:~(main)$ fping -A -c 1 www.torproject.org 116.202.120.165 : [0], 64 bytes, 112 ms (112 avg, 0% loss) 116.202.120.165 : xmt/rcv/%loss = 1/1/0%, min/avg/max = 112/112/112 (It should also be noted here that fping *can* use both IPv4 and IPv6 transparently, see the `-m` option, so the above quote is actually incorrect.)