[server] External network not available

Hello everyone,
I got some problem with my network on a server.
Here is the configuration.
I got 2 ubuntu server as VM. Both same version (15.10), updated at the same time before problems appeared.
The first one is ok, everything is fine.

The second one is messy.
I can access the web site from outside.
I can coect from outside.

But when I'm coected I can not go outside. "ping 8.8.8.8" does not work, as any dig command (coection timed out, even with dig @8.8.8.8)
I compared my resolv.conf file with the good one, it's the same.
Etheet is up
The network configuration from the server (proxmox) are the same for both VM

I supposed first that some application was blocking me, but I stopped almost all applications ruing non-system

I don't know where to look. I didn't find something already posted about this (people can ping an ip address or they have no network at all)

Does someone have some tips for a better investigation ?

Thanks in advance.