I’m adding the answer publicly here (in addition to my answer to your email @mweissprog ) so it can be shared with other Jenkins users.:
The Jenkins Update Center has multiple public IPs which may change over time. We try to avoid the changes as much as possible of course but we can’t be 100% sure.
It is most probably the reason of the issue you have: only one of the IPs is allowed.
The reason is that Update Center is in fact a mirror redirector and usually emits an HTTP redirects to an update center mirror close to your location.
Good news though, we provide an API, a bit lik the “GitHub meta API” which shows the IPs in use and it is updated daily:
The URL https://reports.jenkins.io/infrastructure/latest/index.json presents a JSON where you can find the values, and its content updated daily (it does NOT mean the IP changes daily. Only the report is regenerated once a day).
The command
curl --silent https://reports.jenkins.io/infrastructure/latest/index.json | jq -r '.["[updates.jenkins.io](http://updates.jenkins.io)"].servers'shows the list of servers which have to be allowed with their IPv4 and IPv6.You can use this API endpoint to at least retrieve the IPs to allow. And even better: automate the firewall updates
