[clug] What could be stopping dhclient from setting the default route?

[Tony Lewis]

I am installing a couple of servers; at the moment, using a very basic 
Ubuntu 20.04 install.  When configuring the network, it selected DHCP 
and showed a valid IP, and I leave it at that. However after booting up, 
there is no default route set.  I can't figure out why it's not being set.

I can add the default route from the command line, and everything works 
until a reboot or until dhclient decides to refresh things. I have used 
wireshark to determine that the default route is being sent from the 
DHCP server, both as an option 3 and as a "Next Server IP Address".

I have tried disabling apparmor (there was indications that a dhclient 
script was getting blocked), and I've tried tweaking parameters in my 
server's dnsmasq config, but nothing seems to help.  I've also upgraded 
everything to the latest Ubuntu 20.04 packages.

Google shows that some people report problems like this, but they aren't 
exactly the same, and most are old.  Either way they don't solve things 
for me.

Any clues?

Tony