Nick Howitt wrote:

Can you reboot and select the previous kernel. Then from the command line doo you know if, by any chance, you are using any of the kmod drivers I have previously supplied? If you are, apart from the kmod-r8168 and kmod-r8169, you will need to source the drivers directly from elrepo.org.

I booted the system into the previous kernel and got the same error! It turned out that the system fails to connect the external network if there is a connected lan link! I had to disconnect lan ports in order for the external port to connect, then reconnect the lans! I don't know what causes this, but I'll open a thread in this forum in case I couldn't figure it out.

Thank you.