Comment 0 for bug 1818527

It seems that when systemd-resolve cache an non-existent CNAME record for a domain, any attempt to resolve A record for the same domain fail.

systemd version the issue has been seen with
Installed: 237-3ubuntu10.13
Used distribution

Distributor ID: Ubuntu
Description: Ubuntu 18.04.2 LTS
Release: 18.04
Codename: bionic

Expected behaviour you didn't see

Return A record for a domain when it exists.

Unexpected behaviour you saw

Resolution failed.

Steps to reproduce the problem

Whait for 1 minutes (github.com TTL for A record)

Try to resolv github.com CNAME record dig CNAME github.com

This will return an empty result.

Then try to resolve github.com A record dig A github.com.

This will now return empty result unless you restart systemd-resolved or wait for cache expiration.

At the same time using another DNS will resolve correctly dig A github.com @8.8.8.8.

Exemple :

Wait for 1 minutes to let cache expire, then run

dig CNAME github.com
dig A github.com
# no result
dig A github.com @8.8.8.8
# ;; ANSWER SECTION:
# github.com. 59 IN A 192.30.253.113
# github.com. 59 IN A 192.30.253.112

PS: Don't forget to restart systemd-resolve, before trying to post an answer.

This bug was first reported in github https://github.com/systemd/systemd/issues/11789 but systemd version in ubuntu is too old.