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?

[BPry]

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.

[sharam]

There are no entries under Policy -> DoS Protection.

Is there another location I can look?

[BPry]

@sharam,

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. 

[sharam]

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

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

[Brandon_Wertz]

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@sharam wrote:

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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You're showing the detailed log entry.  (You've clicked the magnifying glass next to an entry in the threat log)  To better help point out why this is happening we need to see the main entry.  It looks like this is happening because of a VP profile which is attached to a security policy rule.

[fhewiufhwefhwe]

zone protection

[sharam]

Thank you for your response @Brandon_Wertz .  This is the main entry of an event that just happened today:

[sharam]

Can you please be more specific?  Zone Pro is the first place we looked and changed various config to no effect.

[fhewiufhwefhwe]

Did you look under Objects -> Security Profiles -> Dos Protection?   Th default block duration is 5 minutes..

[sharam]

@fhewiufhwefhwe there are no entries under Objects -> Security Profiles -> Dos Protection, not even default.

[fhewiufhwefhwe]

Do you have source address exclusions under Reconnaissance Protection?  You may want to include highly trusted items on your allow list there, such as internal DNS forwarders if you have them.

[sharam]

We don't have this problem with UDP which is what DNS uses.

[fhewiufhwefhwe]

DNS does use UDP, but can also use TCP over port 53 as well.  Any way if you have site-to-site vpn or something similar, you may want some exclusions to Dos / Zone protections policies.

[sharam]

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.