WCF Service: Status 200 with sc-win32-status of 64

Question

We observed the following behavior on one of the servers hosting a WCF service on IIS 6.0:

1. The IIS log shows a high value for time-taken (> 100000)
2. The HTTP status code is 200
3. sc-win32-status code shows a value of 64

I found out that sc-win32-status code of 64 indicates "The specified network is no longer available"

Initially I suspected that it could be because of limits set on MinFileBytesPerSecond, which sets the minimum throughput rate that HTTP.sys enforces when sending data from the client to the server, and back from the server to the client. But the value for sc-bytes and cs-bytes indicate that the amount of data is sent is within the range generally observed for the service.

Also note that the WCF service is hosted on four boxes and is load-balanced, but the problem occurs only one of the servers. (but not essentially on the same server). The problem is also intermittent.

Has anybody else encountered this error? Any clues about what could be wrong?

Update

Note: Observation on IIS 7.5 (IIS version does not really matter)

I was able to replicate the issue. The issue occurs if:

1. The WCF service takes a long time to respond
2. The client proxy times out before it receives a response from the server. In this case it leads to TimeoutException on the client.
3. The server keeps waiting for TCP ACK for the client, which it would never receive.

Hence a long timeout (TCP socket timeout (default value: 4 minutes) and sc-win32-status of 64

So essentially it appears that WCF code is taking a long time to respond and the client is timing out, what I observe in IIS log is just a symptom and not a problem.

Answer 1

The behavior you are describing will also occur if you exceed a WCF service's max sessions, calls or instances (depending on how you have your service instancecontext mode configured). If you observe the System.ServiceModel performance counters for %max concurrent sessions and/or %max concurrent calls (again depending on your service's instance context), you may see a correlation with the IIS log entries.

Note that these maxes can be configured in the service throttling behavior.

https://msdn.microsoft.com/en-us/library/vstudio/system.servicemodel.description.servicethrottlingbehavior(v=vs.100).aspx