An Ubuntu 14.04 server acting as gateway. Services DHCP, DNS name server for many domains, Ossec, Asterisk/Freepbx. Periodically, for several minutes at a time, all outgoing traffic is dropped. Then the connection starts working again without my doing anything. This happens many times per day. Cannot ping a public IP address while this is going on. Voip: incoming traffic appears to work, can hear the other party, but they do not hear me. I replaced the ETH0 nic and have examined syslog but have not been able to find a cause. Looked at DNS and DHCP functions. There are strange things going on with DHCP. One of the workstations says it lost its IP address but it doesn't seem to lose it's connection in relation to that message. Not sure where to look for the problem.