Missing Header - Old agent (2.2.9) on Zabbix 6.0.4

[highway_fixer_man]

Hi Guys,

Due to reasons I wont get into - I have over 100 hosts running Debian 6 (Please don't stop reading - they are in the process of being eliminated, this is part of that project) - but I need to keep an eye on these guys for a while still.

Digging through old packages, I found the 2.2.9 agent that works on Debian 6. I read around here, and confirmed that this agent should work with Zabbix 6 - https://www.zabbix.com/forum/zabbix-...ts-and-servers

I am testing this on one host to start with. I have the Zabbix Server up and running - it seems quite happy.

We are getting issues with the connectivity between the agent and the server. I have been assured that the firewall is open between the two hosts when testing. The network engineer who is managing this side of things assured me he troubleshot with the appropriate firewall rules in place. Due to security, these rules have now been removed, but can be put back in place as needed (all traffic between the two hosts are allowed when these rules are in place)

In the /var/log/zabbix/zabbix_server.log file - I see something of much interest (I am changing the IP (192.168.0.10) and zabbix server hostname (zabbix-master) for sake of company policy):


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root@zabbix-master:/etc/apparmor.d# grep 192.168.0.10 /var/log/zabbix/zabbix_server.log
458970:20220725:142545.443 Message from 192.168.0.10 is missing header. Message ignored.
458971:20220725:142640.535 Message from 192.168.0.10 is missing header. Message ignored.
458971:20220725:144311.682 Message from 192.168.0.10 is missing header. Message ignored.
root@zabbix-master:/etc/apparmor.d#

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In other posts, I have seen this error is due to the agent being of a newer, incompatible version as the server - so agent version higher than server version - but this is not the case here. This is an "old" agent, talking to a "new" server.

Am I missing something? Do I need to change anything to get the agent to talk to the server?

Any suggestions or advise would be very appreciated.



EDIT: Adding the log line from the agent logs that looks suspicious (replaced IP with Zabbix Server hostname as to obfuscate the real IP):

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17019:20220725:144354.930 active check configuration update from [zabbix-master:10051] started to fail (ZBX_TCP_READ() failed: [4] Interrupted system call)

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[highway_fixer_man]

This was in fact, a networking issue.

Markku was right.

I am able to use the agent version2.2.9 with Zabbix 6.

[vladimir_lv]

Hi!
It doesn't matter which one is older: server or agent. Your difference between the agent and the server is huge. Starting from the 4th version header use is mandatory:

Support for the plain text protocol has been dropped and a header is now mandatory. A header has been added to Zabbix get requests, Zabbix server/proxy passive check requests and frontend requests to Zabbix server.

https://www.zabbix.com/documentation/4.0/en/manual/installation/upgrade_notes_400#plain_text_protocol_dropped

[highway_fixer_man]

Thank you for the response, vladimir_lv


I found a reddit post suggesting my issue was that I had not assigned a template to the host (its been a while) - after assigning a template to the host, the "missing header" message has gone away from the Zabbix server logs. So I am not sure if I have solved a problem, or hidden it away - although I am leaning to the former here.

Reading the link you posted, the line after the line you posted says:

As a consequence, Zabbix agents that are older than version 1.4 are no longer supported. Also, messages from self-written senders will be rejected if the header is absent. Whereas previously Zabbix trappers would accept messages without headers as well as messages with headers, now they will only accept messages with protocol header.

As I am using 2.2.9 - I would expect this to work.

Now that I have cleared the "missing header" message - I am looking at the next, which is "11878:20220726:100535.332 active check configuration update from [zabbix-master:10051] started to fail (cannot connect to [[zabbix-master]:10051]: [4] Interrupted system call)" <- this feels like a networking issue to me, but I cant be certain.

Any assistance or advice appreciated. I think it might be worthwhile that I document my adventure, and perhaps post it as a topic - it might be helpful.

[Markku]

"11878:20220726:100535.332 active check configuration update from [zabbix-master:10051] started to fail (cannot connect to [[zabbix-master]:10051]: [4] Interrupted system call)" <- this feels like a networking issue to me, but I cant be certain.

Yes, can also be some kind of firewall rule or inspection that resets/drops the connection.

Markku

[highway_fixer_man]

This was in fact, a networking issue.

Markku was right.

I am able to use the agent version2.2.9 with Zabbix 6.