Hi. While I don't mind clarifying the server ID discussion, I don't see that server ID has any relation to how the peer validates the name in the server certificate. Quoting section 7.6: 7.6. Server Certificate Validation
As part of the TLS negotiation, the server presents a certificate to the peer. The peer SHOULD verify the validity of the EAP server certificate, and SHOULD also examine the EAP server name presented in the certificate, in order to determine whether the EAP server can be trusted. When performing server certificate validation implementations MUST provide support rules in [RFC5280] for validating certificates against a known trust anchor. In addition, implementations MUST support matching the realm portion of the peer's NAI against a SubjectAltName of type dNSName within the server certificate. However, in certain deployments, this might not be turned on. Please note that in the case where the EAP authentication is remoted, the EAP server will not reside on the same machine as the authenticator, and therefore the name in the EAP server's certificate cannot be expected to match that of the intended destination. In this case, a more appropriate test might be whether the EAP server's certificate is signed by a CA controlling the intended domain and whether the authenticator can be authorized by a server in that domain. According to that text checking against a DNS name SAN is the mandatory-to-implement naming check for server certificates. That seems adequate to me.