def METHOD_NAME(self, asn: int, prefix: str = "auto", aac: AddressAssignmentConstraint = None) -> InternetExchange:
    """!
    @brief Create a new InternetExchange.
    @param asn ASN of the new IX.
    @param prefix (optional) prefix of the IX peering LAN.
    @param aac (optional) Address assignment constraint.
    @returns created IX.
    @throws AssertionError if IX exists.
    """
    assert asn not in self.__ixes, "ix{} already exist.".format(asn)
    self.__ixes[asn] = InternetExchange(asn, prefix, aac)
    return self.__ixes[asn]