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  • :(){ :|:& }:
    Junior Member
    • Jun 2017
    • 2
    #1

    Issue with IPv6 = False Positive

    Hello gents!

    I installed Zabbix some days ago and I have an issue that I haven't resolved yet..
    As CloudFlare use IPv6 as DNS, I have a bunch of false-positive Alerts from Zabbix.
    Under the same minute I receive an Alert and it recovery, several times a day.

    Here's the output from latest data about the issue:
    Code:
    06/11/2017 04:00:56 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/11/2017 01:44:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/11/2017 01:43:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/11/2017 01:33:40 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/11/2017 01:00:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/10/2017 06:45:06 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/09/2017 05:57:23 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/09/2017 10:48:26 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/08/2017 11:59:39 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable

    Something can be done with Zabbix configuration to fix it? Someone else got hit by this problem before?
    I disabled IPv6 on my servers and I use an active agent (if that can help)

    I use zabbix 3.2.6

    Thank you for your time =)
    Last edited by :(){ :|:& }:; 13-06-2017, 15:25. Reason: I added the zabbix version
    Tags: false alarms, false alerts, false positives, ipv6, unreachable
    • batchenr
      Senior Member
      • Sep 2016
      • 440
      #2
      Originally posted by :(){ :|:& }:
      Hello gents!

      I installed Zabbix some days ago and I have an issue that I haven't resolved yet..
      As CloudFlare use IPv6 as DNS, I have a bunch of false-positive Alerts from Zabbix.
      Under the same minute I receive an Alert and it recovery, several times a day.

      Here's the output from latest data about the issue:
      Code:
      06/11/2017 04:00:56 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/11/2017 01:44:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/11/2017 01:43:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/11/2017 01:33:40 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/11/2017 01:00:05 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/10/2017 06:45:06 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/09/2017 05:57:23 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e01b: Network is unreachable
06/09/2017 10:48:26 AM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable
06/08/2017 11:59:39 PM	
Couldn't connect to server: Failed to connect to 2400:cb00:2048:1::6819:e11b: Network is unreachable

      Something can be done with Zabbix configuration to fix it? Someone else got hit by this problem before?
      I disabled IPv6 on my servers and I use an active agent (if that can help)

      I use zabbix 3.2.6

      Thank you for your time =)
      i can only suggest to maybe build a trigger to be based on checking the last 10 values (or how much you want) and if more then 5 is like this then alert.

      somthing like this
      {host:item_key.count(#10,"Failed to connect","ne")}>5

        Comment

        • :(){ :|:& }:
          Junior Member
          • Jun 2017
          • 2
          #3
          Thank you batchenr for your suggestion.

          We found the root cause of this issue and itsn't a false-positive alert, we really had an issue with ipv6 checks.

          As we disabled all ipv6 on our servers and our Zabbix proxy monitors our websites from an external point of view (public), the name resolutions is done by CloudFlare and their IPv6-only DNS.

          After a deeper investigation from our side, we found the libcurl version used by CentOS 6.9 (7.19.7). A known bug still exist on this libcurl version about "Can't curl hosts with both IPv4 and IPv6 addresses"
          The bug has been fixed in curl-7.20.1-1.fc13 but CentOS not applied this patch to CentOS6.9

          We fixed the problem by modifying this file and recompiling:
          zabbix-3.2.6/src/zabbix_server/httppoller/httptest.c

          In big picture, we deactivated IPv6 from Zabbix server (see attachment)
          Attached Files

            Comment

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