This is somewhat of an update/continuation of the following thread:
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Basic rundown is that the 'ip inspect' functionality on a 2811 ISR (12.4) starts at 500/400 connections before it starts dropping and resetting communication. I upped this 500/400 default value to2000/1900 and everything was fixed and worked for about 3 months. I get another call today with the same symptoms and sure enough: