All of the links you provided are inaccessible to me from my home network. I encountered this issue when trying to login via cloudsso.cisco.com.
Like with you, I previously had no problem accessing these URLs. I don't use them frequently, but it's definitely within the last couple of months where they became inaccessible.
I stumbled across this forum post while desperately searching for anyone else complaining about being unable to reach cloudsso.cisco.com. This is the first and only one I've found, but it matches my experience exactly, down to the relative timing of when the site(s) stopped being reachable.
My home broadband provider is Comcast/Xfinity.
Some things I have discovered while troubleshooting:
If I take my entire home network out of the equation and plug a laptop directly into my cable modem, I am able to access cloudsso.cisco.com. Once I add a router back into the equation, the site becomes inaccessible again.
I have replaced my original router (TP-Link TL-R605) with a mini-PC running pfSense, no fix. The specific router does not appear to be the issue, although I intend to dig up at least another one or two to test.
I disabled every security feature I could find in the TP-Link, but nothing made a difference. I am working my way through pfSense config changes, but I am less familiar with them.
DNS does not appear to be the issue. I have tried using many different DNS providers. They all resolve the hostname to the appropriate IP, but I am simply not able to get any of my traffic to route to the address.
Using a VPN service, like PrivateInternetAccess, instantly makes cloudsso.cisco.com accessible again.
My home network uses 10.10.10.x for its IP block. I can't imagine this would make any difference. Switching it back to a 192.168.x.x did not solve the problem.
Like you, I speculated that my cable modem's public IP address might have been blocked somehow. But the fact that I could access the site if I removed any router and plugged directly into my cable modem invalidated that theory. For whatever reason, adding that extra "hop" of a router renders those sites inaccessible.
EDIT: cloudsso.cisco.com resolves, alternatingly, to 126.96.36.199 and 188.8.131.52. In pfSense, I see the failed attempts at sending traffic to these addresses, here's a representative sample (the 24.x.x.x is my cable modem public IP, I've redacted it for privacy reasons):
PR DIR SRC DEST STATE AGE EXP PKTS BYTES
tcp In 10.10.10.182:58762 184.108.40.206:443 CLOSED:SYN_SENT 00:00:22 00:00:23 5 260
tcp Out 24.x.x.x:54826 220.127.116.11:443 SYN_SENT:CLOSED 00:00:22 00:00:23 5 260
tcp In 10.10.10.182:58764 18.104.22.168:443 CLOSED:SYN_SENT 00:00:22 00:00:23 5 260
tcp Out 24.x.x.x:31201 22.214.171.124:443 SYN_SENT:CLOSED 00:00:22 00:00:23 5 260
tcp In 10.10.10.182:58761 126.96.36.199:443 CLOSED:SYN_SENT 00:00:22 00:00:23 5 260
tcp Out 24.x.x.x:8162 188.8.131.52:443 SYN_SENT:CLOSED 00:00:22 00:00:23 5 260
tcp Out 24.x.x.x:7532 184.108.40.206:443 SYN_SENT:CLOSED 00:00:27 00:00:18 5 260
tcp In 10.10.10.182:56590 220.127.116.11:443 CLOSED:SYN_SENT 00:00:27 00:00:18 5 260
tcp Out 24.x.x.x:42323 18.104.22.168:443 SYN_SENT:CLOSED 00:00:27 00:00:18 5 260
tcp In 10.10.10.182:56591 22.214.171.124:443 CLOSED:SYN_SENT 00:00:27 00:00:18 5 260
tcp Out 24.x.x.x:3793 126.96.36.199:443 SYN_SENT:CLOSED 00:00:27 00:00:18 5 260