1 system will not talk to Nagios

[JohnFLi]

Nagios: 2026R1.5

migrating Nagios from 1 OS to a different OS

working system:
Centos7
2026R1.5

not working system
Ubuntu 24.04
2026R1.5

Migration went fine...nothing major.
after migration, renamed the new machine to the same name as the old machine....gave it the old IP address as well.

ALL hosts and services are happy----------- EXCEPT 1
sometimes it will talk to it and say a service or a check is good, other times it says it can't talk to it.
i ran https://servername:5693/testconnect/?token=123456
on the client machine, is was happy

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{
  "value": "Success."
}

ran the same on the new nagios machine.....it also said it was happy

so i delete the trouble maker out of nagios. ran the wizard for the windows machine (2019)
I enter the name for the server, leave the port as default and enter the token

it thinks for a few moments, then returns:

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Connection timeout.  Failure connecting to NCPA {GDFNA:001]
E_WARNING:  http://servername:5693/api/disk?token=<your_token>
Failed to open stream
Connection Time out

for fun, i disable the nic on the NEW nagios machine, re-enable the nic on the OLD nagios machine....

and it talks just fine.
Tells me there is somethign on the unbuntu machine that is the issue....any ideas??

[cdietsch]

Hi @JohnFLi,

This sounds to me like some sort of networking issue on the new Ubuntu 24.04 XI server. Are you by chance using IPv6 or a mix of IPv6 and IPv4? Are you trying to resolve a hostname and not an IP address from the XI Wizard? It could be there are both IPv6 and IPv4 namerecords and there is some type of issue going on there.

Here are some commands that might be helpful troubleshooting this issue:

Run on Ubuntu:

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getent ahosts servername

or

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dig servername
dig AAAA servername

If you see IPv6 entries, test:

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curl -4 https://servername:5693/api/system/agent_version?token=mytoken -k

and:

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curl -6 https://servername:5693/api/system/agent_version?token=mytoken -k

If -4 works and -6 hangs → found it.