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NameBasedSSLVHosts - Httpd Wiki
As a rule, it is impossible to host more than one SSL virtual host on the same IP address and port. This is because Apache needs to know the name of the host in order to choose the correct certificate to setup the encryption layer. But the name of the host being requested is contained only in the HTTP request headers, which are part of the encrypted content. It is therefore not available until after the encryption is already negotiated. This means that the correct certificate cannot be selected, and clients will receive certificate mismatch warnings and be vulnerable to man-in-the-middle attacks.