DBA Tactics for Optimizing SQL Network Performance

ASYNC_NETWORK_IO is defined as a wait for completion of a network write. This could be an indicator of a bottleneck somewhere in the network between SQL Server and the reader of the data. In most cases, the root cause can be traced to the reading client performing paged reads or simply reading the data slower than SQL Server can send it. If there is a network issue, it may show in this wait type as well.

The trouble with network bottlenecks is that DBAs typically have very little insight into the network. There are a handful of performance counters that we can track with Performance Monitor (PerfMon) or the Dynamic Management View (DMV) sys.dm_os_performance_counters. The counters can help you determine that there may be a problem through baselining and looking for patterns where the counters skew from the norm. But they don't really help you determine where the issue lies when it is a network bottleneck.