All incoming TCP connections blocked for 5 minutes at random times.

[sharam]

At random times all TCP connections from the Internet are blocked (all ports and all IPs) for incoming traffic only.  Websites, mail servers etc are not accessible from the Internet.  UDP and ICMP are not affected.  What could be causing this?

[fhewiufhwefhwe]

Example of SNMP monitoring.  That being said, it is painful / somewhat manual to setup.

[sharam · Accepted solution]

Thanks to all who responded.  I was finally able to resolve this problem by by changing zone protection for Untrust from SYN Cookies to Random Early Drop.