How do I know if a connection goes down in a load balancing router?

Question

I am using a TL-R470T+ load balancing router to combine my two broadband connections. Is there a way I can know as soon as one of the broadband lines goes down?

My approach so far:

I have tried to set up policy routing to figure out a solution. I picked up two IPs. I assigned the first IP to use only WAN1, and the second IP to only use LAN2. I created a script which keeps pinging both IPs and alerts me if one of them doesn't work.

However I realize that as soon as WAN1 goes down the first IP starts using WAN2. Hence, I never come to know that WAN1 has gone down.

Is there a solution to this?

Answer 1

You have two options:

Enable SNMP on the router and use SNMP protocol to monitor the WAN link.

Enable event log forwarding on the router.

Answer 2

Load balancing routers should have methods of detection. Usually, they can be configured to ping an external IP and therefore detect when a line is down. Additionally, they can be configured to send an alert when a line is down.

Your script should also be viable if done properly, because there will be a packet loss when the lines switch, therefore you will be able to detect the downed line.

Answer 3

Use tracert to view the first few hops of a ping to an external server. You can check the results in a script and easily determine which connection is being used.

I created a PRTG plugin where I work that does exactly this and it has worked a treat for years.