Do Modems with Same IP Address Interfere When Connected to Same Router?

modemNetworkpfsenserouterwan

Here is information about the network:

  • I have 2 WAN connections to the same ISP which they provided 2 modems
    for and configured them to be in bridge mode.
  • My MDF router (pfSense) connects both of them through two
    different physical interfaces.
  • One interface is configured for DHCP and the other is static, with a static IP and gateway provided by my ISP.
  • The WANs are setup to be load balancing on the router (which works as expected).
  • From the pfSense web GUI I can see the interfaces get their public IP address & gateway addresses.
  • I have a LAN network of a typical 192.168.1.0/24, but I can still access
    the web interface for these modems at 192.168.100.1.

Since their web interfaces are both accessible through 192.168.100.1, although they are connect to different interfaces on the same router, can they interfere with each other and kick each other offline?

I am having connectivity issues, latency, and packet loss when they are connected at the same time, but do not seem to have as much of an issue when I have one at a time connected.

Best Answer

There's only a problem when they're on the same wire ("broadcast domain") -- but it won't stop either modem from working. And it's only a problem for you as you won't know which one will respond. Which ever one your system accepts as the answer to the ARP request will be the one you're talking to. As they're on separate interfaces, which one you talk to is up to routing -- which ever link the load balancing selects will be the modem you see, and that could change unpredictably.

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