I am intermittently seeing the Performance Counter of ISA Server Firewall Service --> Available Worker Threads = 0.
When this happens, web clients Internet surfing slows to crawl. Everything from DNS resolution to RDP sessions slow to a crawl as well.
I have verified that CPU utilization remains below 5%, Page Faults are lows, network utilization is low, Pending DNS resolution counters are 0, Pending TCP connection counters are 0, Disk I/O is low. I cannot find anything wrong with the box. The network team has looked at the switch ports connecting to these ISA servers and there are no errors there either.
Can anyone tell me how to investigate the causes of "Available Worker Threads" going down to 0 on an ISA server? I'm out of ideas.