Network Interface Down!!!

In this morning, my server was disconnect. It shows message as below.

8 08:02:02 dhcpcd[5572]: timed out waiting for a valid DHCP server response
08:02:02 dhcpcd-hook: Skipping ‘ifdown $INTERFACE -o dhcp’ call
08:02:02 kernel: bonding: bond0: link status definitely down for interface eth0, disabling it
08:02:08 dhcpcd[7104]: timed out waiting for a valid DHCP server response
08:02:08 kernel: bonding: bond0: link status definitely down for interface eth3, disabling it
08:02:08 dhcpcd-hook: Skipping ‘ifdown $INTERFACE -o dhcp’ call
08:02:13 dhcpcd[7602]: timed out waiting for a valid DHCP server response
08:02:13 kernel: bonding: bond0: link status definitely down for interface eth5, disabling it
08:02:13 kernel: bonding: bond0: now running without any active interface !
08:02:13 kernel: bonding: Warning: No 802.3ad response from the link partner for any adapters in the bond
08:02:13 dhcpcd-hook: Skipping ‘ifdown $INTERFACE -o dhcp’ call

I must manual turn on this interface. Then it’s ok.

My question is what is the cause of this issue. How can I fix it?

Thanks for your help

Seems that it was as it says: DHCP server not answering.

Does it do this all the time or just this morning?