I have the whole internet again.  Thank you all for your infinite
   patience.
   On Tue, Dec 15, 2020, 11:16 AM coderman <[1]coderman@protonmail.com>
   wrote:

     ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
     On Tuesday, December 15, 2020 12:30 AM, Karl <[2]gmkarl@gmail.com>
     wrote:
     ...
     > i can get to the real internet on wifi using my phone in airplane
     > mode, so obviously my linux system has a virus that blocks the
     > internet. sorry for the big alarm. need to archive this thing and
     > eventually figure out how to do incremental backups of a new
     system.
     definitely weird behavior.
     no route is messing with your route tables - you can view these.

   I'm on a local-only network that for some reason is being given a
   default route by networkmanager.  There are two default entries in my
   routing table.  The issue goes away when the local one is removed!
   Thanks so much; I get so confused.

     odd to get a DHCP lease, and IP, but no route.
     can you log into the router itself to check logs?

   I was surprised to find so few open source cable modems, and such small
   development communities around them, back when I had one.  It's an
   xfinity router.  But I could have run a sniffer on another system.

     can you run a traceroute on the Linux system to see where the drop
     is?

   This reveals the issue.  Traceroute resolves ipv4 addresses and
   requests all seem to terminate at the wrong interface.  Curl is
   resolving ipv6 addresses which get routed to the wan interface.  It
   seems the websites and ips that didn't work were the ones without ipv6
   addresses!

     i like to manually set DNS servers, rather than use ISP nameservers.
     try switching those out. (e.g. 4.2.2.4, 4.4.4.4, 1.1.1.1, etc.)
     [ but to be fair, this is a routing issue, not DNS, but DNS problems
     might be up next... ]

   Good thoughts.

     have you tried turning the router off and on again? :P

   Yeah I had done that ;p

     good luck!
     best regards,
     ------
     [3]https://unix.stackexchange.com/questions/50098/linux-network-trou
     bleshooting-and-debugging
     [4]http://www.ruf.rice.edu/~rlug/help/net-debug.html
     [5]https://wiki.archlinux.org/index.php/Network_Debugging
     [6]http://www.thegeekstuff.com/2011/12/linux-performance-monitoring-
     tools/
     [7]https://web.archive.org/web/20160128084542/http://www.linuxdoc.or
     g/HOWTO/NET3-4-HOWTO.html

References

   1. mailto:coderman@protonmail.com
   2. mailto:gmkarl@gmail.com
   3. https://unix.stackexchange.com/questions/50098/linux-network-troubleshooting-and-debugging
   4. http://www.ruf.rice.edu/~rlug/help/net-debug.html
   5. https://wiki.archlinux.org/index.php/Network_Debugging
   6. http://www.thegeekstuff.com/2011/12/linux-performance-monitoring-tools/
   7. https://web.archive.org/web/20160128084542/http://www.linuxdoc.org/HOWTO/NET3-4-HOWTO.html