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

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

L2 Linker

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?


Accepted Solutions

L2 Linker

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.  

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Cyber Elite
Cyber Elite

Sounds like a DoS profile that is setup incorrectly and is blocking the destination address (your public IP) or vulnerability protection profile with the same misconfiguration. The default block-ip timeout is 5 minutes, which lines up with what you are running into.

There are no entries under Policy -> DoS Protection.

Is there another location I can look?


If you had any that's where they would be. What does your Vulnerability Protection profile look like for the security rulebase entries allowing this traffic inbound? That would be the next thing I would look at. 

What I am seeing in logs related to the outage is:



But I am not able to see which rulebase this it related to.

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