Router's LAN plugged directly into the Internet (its public WAN)

  • I know just enough about networking to believe that this is a bad idea.

    What happens when you plug the LAN (private subnet) from a router's integrated switch back into the WAN which is the internet. (In this case the router is assigned a public static IP and a CIDR of 28 bits if that helps describe the WAN)?

    I can't help but think that an ISP would be unhappy about having a DHCP server on their network. I also assume that devices (even if in a private subnet) would be subject to attack. It just seems wrong, but I can't really put my finger on why in a way that the person who did this is accepting.

    Suggestions on how to advise them to plug their Internet connection into the WAN port on their crappy router and leave the LAN isolated behind it? Or am I being naive and there's a reason to do what they're doing?


  • At least ISP should be blocking private ip-areas and they should have protected dhcp services.

    Nevertheless that is always bad idea, unless you're having a router connected to public ip-area.

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