Hi. 

We have 2 connections on our ONT, one PPPOE (port1) and one DHCP (port2)

We are connecting a Fortigate to the third port.  It's a DHCP enabled connection. 

If we connect the same firewall to the DHCP enabled second port, we get an immediate connection. 

Essentially according the provider, the Firewall sends a request, gets an acknowledgement, sends another request and eventually after back and forward for a bit, won't connect and throws an error. 

We have disconnected ports 1 and 2 and restarted the ONT, no change. 

Anyone seen anything similar?