I am experiencing long DNS lookup times (> 5s) due to non-compliant EDNS responses from my DNS server triggering (I think) this bug in systemd-resolved. I'd like to turn off EDNS in resolved to see if that fixes the problem, however I have been unable to figure out how to do this.
/etc/resolv.conf is a symlink to
/run/systemd/resolve/stub-resolv.conf and contains the line
options edns0 trust-ad. I have tried removing the symlink and replacing it with a real file that does not have this "options" line and then restarting resolved, however after doing that I still see the following log message in syslog:
Feb 15 09:07:35 charon systemd-resolved: Using feature level UDP+EDNS0 for transaction 31630.
What is the correct way to disable EDNS in resolved on Ubuntu 20.04?