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?
Thanks @fhewiufhwefhwe but the problem we are facing is that when the TCP outage occurs our thousands of user who are scattered across the Internet world are not able to reach our websites or mail servers. We don't want the firewall to block the whole Internet.
I should also point out if the subject is not clear that the problem is only with incoming TCP traffic. Outgoing traffic is not affected.
Have you tried increasing the thresholds under SYN Flood Protection then? How high is your firewall on resource utilization? I'm wondering if you might be able to use SYN Cookies instead of Random Early Drop action? Note that I have not tried this myself.
I'm also thinking that you might want to setup SNMP monitoring the DoS counters on the firewall. I recently tried to configure this, but have not had success yet.
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