I have a Cisco 1811 router with 2 Ethernet Ports and 1-9 FastEhernet ports( 1-9 act like a switch).On the Ethernet port I have trunked to my ISP for my private network. And on the FastEthernet1 is the firewall , FastEthernet3is the Cisco Concentrator and FastEthernet6 ISP internet connection is connect. There is default vlan 1 on the FastEthernet 1-9 .When I reboot the firewall the FastEthernet1 goes downas per normal but the LINE PROTOCOLwhere the Concentrator is connect goes down as well and does not come up until I log on to the concentrator and ping out from that port.
The Firewall has a public IP address and the Concentrator has a public IP address but they are on different subnets. The ISP router has the firewall subnet as primary and the Concentrator as secondary.