HTTP2_PROTOCOL_ERROR in Synthetic Monitor

GerardoAud — Thu, 03 Jul 2025 07:41:42 GMT

Hello,

I've set up a Synthetic monitor from a private location to check system availability, and it generally works well. However, occasionally I encounter the following error, which negatively affects the availability score:

Error Code: 12143 - The site reported HTTP2 PROTOCOL_ERROR

I found this suggestion in the community:

"May be caused by firewalls like Akamai. In these cases, add Synthetic Browser Monitor traffic to the firewall allow list."

A few follow-up questions:

What exactly might a firewall (like Akamai or others) block that would trigger this HTTP2 protocol error?
Are there known parameters in synthetic traffic that can cause firewalls to interfere?
Could someone confirm if this error is reliably firewall-related or if it could be caused by other network issues?

@HannahM, can you help here with this?

Attached are screenshots with error details from the Synthetic execution.

Thanks in advance!

Re: HTTP2_PROTOCOL_ERROR in Synthetic Monitor

HannahM — Thu, 03 Jul 2025 12:18:26 GMT

Akamai is likely recognising 'RuxitSynthetic/1.0' from the User Agent header and marking us as a bot. So, allowing that should be enough. Otherwise, it can be that it sees a pattern of traffic from your location, so you may also need to exclude your IPs from this check.

We added the suggestion to the guide because we found that Akamai sometimes blocks our Synthetic traffic, and we needed to add exclusions to prevent this.

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HTTP2_PROTOCOL_ERROR in Synthetic Monitor

Re: HTTP2_PROTOCOL_ERROR in Synthetic Monitor