I need to configure a modem for my asdl connection. I have 4 public ip to manage:

  • 1 for my modem

  • the others for servers that are on my LAN

The situation is this:

modem with public ip

My problem is: which is the configuration that I need to apply to my modem? I mean, what is the technique that I need to apply?

Thanks a lot!

  • Unfortunately, questions about home networking and consumer-grade devices are explicitly off-topic here. You could try to ask this question on Super User.
    – user36472
    Commented Feb 8, 2018 at 11:15
  • Hello Bau Miao, welcome to Network Engineering S.E. Please keep in mind that SOHO devices like your Fritzbox are off topic here. So we can answer to the question about the techniques to be used, but not about your modem configuration. It could also be debated if it's a good idea to have Internet facing servers behind such a device, without a true firewall.
    – JFL
    Commented Feb 8, 2018 at 12:07
  • Hi JFL! Ok I'm agree! The real target of my question is about the techniques. I have put the model of the modem only to be exhaustive.
    – Bau Miao
    Commented Feb 8, 2018 at 13:58
  • Sadly, consumer grade equipment is also off-topic. Super User is the place to ask this question.
    – Ron Trunk
    Commented Feb 8, 2018 at 14:00
  • I have cut off the modem model.
    – Bau Miao
    Commented Feb 8, 2018 at 14:25

1 Answer 1


This is basic routing, a function that normally routers perform by default, without any special configuration other than setting the IP addresses on the interfaces.

Assuming the ISP take care of routing the 4 public IP addresses to your router, all you have to do is set the IP addresses on the servers and the router, and configure the router with whatever default route your ISP gave you.

SOHO routers have NAT enabled by default, and it is not needed if you set the IP addresses on the servers, so in this case you would have to disable it.

You also need to configure at a minimum some access list to filter the traffic that can reach the servers in addition to have the local firewall of each server properly configured.

  • Perfect. Thanks a lot JFL. My concern was about any advanced features that the router needed to have.
    – Bau Miao
    Commented Feb 9, 2018 at 10:09

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