I have ipv6 disabled on my network, so that will always fail:
$ curl http://ipv4.whatismyip.akamai.com/ ; echo
43.225.60.184
$ curl http://ipv6.whatismyip.akamai.com/ ; echo
curl: (7) Couldn't connect to server
$ dig +short whoami.ipv4.akahelp.net TXT
"ns" "172.68.116.82"
$ dig +short whoami.ipv6.akahelp.net TXT
"ns" "2400:cb00:26:1024::6ca2:f884"
$ dig +short whoami.ds.akahelp.net TXT
"ns" "2400:cb00:26:1024::6ca2:f85a"
$ mtr -c 20 -w -r acme-v02.api.letsencrypt.org
Start: Wed Sep 12 11:10:30 2018
HOST: fuller Loss% Snt Last Avg Best Wrst StDev
1.|-- edge 5.0% 20 0.6 0.6 0.4 0.8 0.0
2.|-- lo0.lns01.470n.act.tsgnl.co 90.0% 20 21.7 18.6 15.4 21.7 4.5
3.|-- 202.137.170.2 90.0% 20 17.6 18.1 17.6 18.6 0.0
4.|-- tengige0-0-0-0.civ-edge901.canberra.telstra.net 90.0% 20 22.5 21.9 21.2 22.5 0.0
5.|-- bundle-ethernet2.dkn-edge901.canberra.telstra.net 90.0% 20 19.7 18.0 16.3 19.7 2.2
6.|-- bundle-ethernet6.dkn-core1.canberra.telstra.net 90.0% 20 15.7 17.7 15.7 19.8 2.8
7.|-- bundle-ether15.ken-core10.sydney.telstra.net 90.0% 20 28.1 28.9 28.1 29.6 1.0
8.|-- bundle-ether1.ken-edge901.sydney.telstra.net 90.0% 20 24.5 24.9 24.5 25.2 0.0
9.|-- 203.50.12.105 0.0% 2 29.1 28.3 27.5 29.1 1.0
10.|-- 203.46.69.49 0.0% 2 50.7 65.6 50.7 80.5 21.0
11.|-- a23-9-148-127.deploy.static.akamaitechnologies.com 0.0% 2 70.5 47.9 25.3 70.5 31.9