New container not reachable until I ping

[Herman]

I have noticed several times that when I create a new container, it is not reachable from the internet.
I can neither ping it or ssh into it on it's static IP address.
If however I go into the console from the web-interface and do a ping to an external address it immediately works from remote too.
Anyone any ideas what may be going on?
I am currenly using the Ubuntu 24.04 template.
Proxmox VE is on the latest version.

 

[t.lamprecht]

Could be a duplicate IP address in the network or possibly also firewall related.

 

[UdoB]

Maybe incoming traffic is blocked by default. When you send data from inside to the outside the first package triggers a rule utilizing "connection tracking". After this initial transmission incoming packets may pass (for a period of time).

This is just a generic idea; as I do not use the PVE firewall mechanism I can't help in detail.

 

[Herman]

Thanks for the replies.
It is certainly not a duplicate IP.
The firewall suggestion is good, going to look into that.
Funny thing is that it only happens on first boot, not on subsequent reboots of the container or the server.
And I haven't checked if the same thing happens on IPv4, all my machines run IPv6.