How to detect WAN gateway is functioning if it is behind a modem?

  • I have two ISPs and one of them is accessable via cable modem.

    Cable modem is working as DHCP client and doing NAT, so there is one more LAN between me and Internet with this ISP. My LAN is, while this additional LAN is Modem has address in this LAN and pFsense is regarding this address as a gateway.

    Once this provider's ISP is down, I can't detect it automatically.

    If I ping it is always UP, because modem is UP. This ISP can be down at the very moment.

    If I ping it is also always UP, because traffic goes via second ISP

    Also I can't know gateway IP behind the modem, because it is provided by DHCP and varies.

    How to accomplish?

  • Set the monitor IP to something like, then it'll ensure it's bound to that interface.

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