This article provides step-by-step instructions for adding an additional ISP link (ISP #2) that will be connected to WAN2, while the existing ISP (ISP #1) remains connected to WAN1. Adding more than one additional ISP works identically.
To add a secondary ISP link, complete the following steps.
Step 1: Add the DNS of the Secondary ISP to the Local Network Configuration
You must make the DNS settings of the new ISP available to hosts within the local network. Otherwise, DNS queries will be routed to ISP #1 where they will be rejected due to access and flood control protection. DNS resolution would be impossible and the Internet would be unreachable from the local network.
Add the DNS servers for ISP #2 to the configuration of your internal network. For backup, you may also add the IP addresses of open domain name servers at the end of the list.
Step 2: Assign a New IP Address from ISP #2 to WAN2
Do not change the network configuration for the existing firewall. Assign an additional IP address from ISP #2 to WAN2.
Step 3: Clear the ARP Cache on the Router for ISP #2
The Barracuda Link Balancer will use the MAC address of WAN2 for packets sent to the router (while using the respective source IP address of the firewall) and packets going into the local network. To make sure that neighboring devices use the correct MAC address, you must reboot the router for ISP #2 to clear its ARP cache.