Unable to reach nodes

Ansible certication course.
mock exam-4, question No.4
not able to reach nodes

ansible -i inventory all -m ping
node00 | UNREACHABLE! => {
“changed”: false,
“msg”: “Failed to connect to the host via ssh: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).”,
“unreachable”: true
}
node01 | UNREACHABLE! => {
“changed”: false,
“msg”: “Failed to connect to the host via ssh: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).”,
“unreachable”: true
}

Hello, @sgundapu
Have you configured public keys of the ansible-controller into those remote system?