Reading ASYNC_NETWORK_IO wait stats
While the ASYNC_NETWORK_IO wait type is usually a consequence of the application design, the network issues can also cause the stockpiling of the ASYNC_NETWORK_IO wait type.

It is advised to check the following, regarding the network issues:


Check network bandwidth between the SQL Server and client
Make sure that all network components between the SQL Server instance and the client, such as routers, switches, cables are properly configured, fully functional and dimensioned according to required bandwidth
Review the Batch requests per second counter values, as this could often indicate the reason for high ASYNC_NETWORK_IO waits
Make sure that Auto Negotiate of the NIC is detecting the network bandwidth properly


Also -checking the NIC bandwidth utilization is prudent, even often overlooked.

Please, take a look at the Reducing SQL Server ASYNC_NETWORK_IO wait type aticle, to get more details on interpreting high ASYNC_NETWORK_IO wait type values.