@bagder All of those except 018.1.1.1 get resolved directly by the OS for me.

root@592cda340524:/# cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux trixie/sid"
NAME="Debian GNU/Linux"
VERSION_CODENAME=trixie
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
root@592cda340524:/# grep hosts: /etc/nsswitch.conf
hosts: files
root@592cda340524:/# getent ahosts 010
0.0.0.8 STREAM 010
0.0.0.8 DGRAM
0.0.0.8 RAW
root@592cda340524:/# getent ahosts 010.1.1.1
8.1.1.1 STREAM 010.1.1.1
8.1.1.1 DGRAM
8.1.1.1 RAW
root@592cda340524:/# getent ahosts 018
root@592cda340524:/# echo $?
2
root@592cda340524:/# getent ahosts 18
0.0.0.18 STREAM 18
0.0.0.18 DGRAM
0.0.0.18 RAW
root@592cda340524:/# getent ahosts 018.1.1.1
root@592cda340524:/# echo $?
2
root@592cda340524:/# getent ahosts 18.1.1.1
18.1.1.1 STREAM 18.1.1.1
18.1.1.1 DGRAM
18.1.1.1 RAW
root@592cda340524:/#