The filter to apply on the results of DescribeCustomerGateways.
            
 Remarks
 Remarks
            Filters can be:
            a. state - The state of the Customer Gateway. (pending,
            available, deleting, deleted).
            b. type - The type of Customer Gateway. Currently the only
            supported type is ipsec.1.
            c. ipAddress - The IP address of the customer gateway's
            Internet-routable external interface (e.g., 12.1.2.3).