def METHOD_NAME(peering_name: Optional[pulumi.Input[str]] = None,
                              registered_asn_name: Optional[pulumi.Input[str]] = None,
                              resource_group_name: Optional[pulumi.Input[str]] = None,
                              opts: Optional[pulumi.InvokeOptions] = None) -> pulumi.Output[GetRegisteredAsnResult]:
    """
    Gets an existing registered ASN with the specified name under the given subscription, resource group and peering.
    :param str peering_name: The name of the peering.
    :param str registered_asn_name: The name of the registered ASN.
    :param str resource_group_name: The name of the resource group.
    """
    ...