The difference between an internal CA issue and a public certificate

Question

@Lucas Song micorsInternal self-built CA certificate mounted on IIS to publish https to the public network, and then accessed by the public network computer will prompt for insecurity, this is why?Please ask, the internal self-built CA certificate hit IIS to publish https to the public network, and then accessed by the public network computer will prompt insecurity, this is due to what principle? Why self-built CA server issued certificates in the public network do not recognize, and the public network SSL certificate binding on the site can display a secure page, access to the outside network can only use SSL wildcard certificate?

In addition, please ask, the company purchased a third-party SSO unified authentication system to do integration, need to call domain-controlled LDAP, LDAPS authentication identity AD user identity information, need to bind domain name information and certificates, this certificate can be my self-issued certificate? If so, would it be okay for me to set up information about several of my domain-controlled servers in the DNS consumer of the certificate? Also hope to teach, thank you!