The strange case of Xfinity login failure

I recently moved and thus had to enable a new Xfinity broadband internet connection at my new place. The connection was enabled and I could access all websites on the web, except for Xfinity’s own customer portal!

Shockingly, this seems to be a common problem with Xfinity customers. I tried everything I could think of and was suggested online: restarting the broadband modem, restarting the wireless router and changing the DNS servers. No dice.

By using rudimentary Linux network tools, it was obvious that when connected from inside Xfinity’s network, the DNS/IP/routing they were doing for customers was screwed up:

$ host oauth.xfinity.com
oauth.xfinity.com is an alias for oauth.g.xfinity.com.
oauth.g.xfinity.com has address 162.150.57.167
oauth.g.xfinity.com has IPv6 address 2001:558:fe16:109:96:114:156:145

$ nslookup oauth.xfinity.com
Non-authoritative answer:
oauth.xfinity.com       canonical name = oauth.g.xfinity.com.
Name:   oauth.g.xfinity.com
Address: 96.114.156.145
Name:   oauth.g.xfinity.com
Address: 2001:558:fe16:109:96:114:156:145

$ ping oauth.xfinity.com
PING oauth.g.xfinity.com (68.87.29.197) 56(84) bytes of data.
^C
--- oauth.g.xfinity.com ping statistics ---
13 packets transmitted, 0 received, 100% packet loss, time 12036ms

Notice how host and nslookup returned different IP addresses. And ping used a third different IP address. And none of those IP addresses were pingable.

In the end, I had to use my cellphone’s mobile data connection to access the customer portal of my home broadband internet provider! The portal opened up fine. Going by the complaints online, Xfinity just does not seem to care about this problem. I have been getting by accessing the portal through my cellphone or through a portable hotspot on my computer.