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I would like to configure my linux box to act as its own router, or maybe the better way to put it is that I want the box to connect to the internet directly with no router. There are some other questions that deal with linux-as-a-router, but these deal with situations where the linux box is actually routing to other computers. This does not apply to my situation, where only the single box is the endpoint. One reason I want to do this is that I need to have my cable modem in bridge mode so that Airport Express will work on it. Also, I would just as soon like to configure the routing (or lack of routing actually) using Linux rather than monkey around with the ISP's web interface to their modem.

Since the box is the endpoint, I assume I do not need internal addresses like 192.168.0.1 because there is no LAN, so my box's IP can just be the public facing WAN IP address. In general I think I only need to set up a few services, like DNS. What are the steps to get the box talking to the bridge?

System is Debian Wheezy. Provider is Comcast XFinity and the modem is an Arris TG862G-CT.

Just to re-iterate. I do not actually need to do any routing. There is no LAN. I just need to get the linux box sending packets out over the bridge. Presumably I need to enter static addresses, or possibly MAC addresses somewhere. I have the MAC address of the modem.

As an example of the basic problem operating in bridge mode, the web interface for the modem is probably sitting at 192.168.0.1 but since there is no router, I have no way to access that address without configuring it somehow.

  • So unlike what you say in your title and at the beginning of your question, and like you correctly state near the end, you don't want to make your Linux PC be a router. What you want is to make your “modem” box not be a router. This may or may not be possible, I don't know anything about this modem model. – Gilles Jun 3 '16 at 22:18
  • @Gilles The modem can be set into bridge mode and acts like any bridge. I am pretty sure this is a straightforward process for somebody who knows a lot about networking, its just I do not know how to configure a box to talk directly to a bridge. It really doesn't matter what the model of the modem is. In theory a linux box should be able to interface directly to any bridge, I just don't know how to do it. I have actually ordered some linux networking books that will explain it, but I am hoping for a quick answer from an expert because the books will take a week or more to get to me. – Tyler Durden Jun 3 '16 at 22:27
  • Ah, so you already know how to make the modem operate in bridge mode? That wasn't clear from your question. – Gilles Jun 3 '16 at 22:30
  • If your ISP "authenticates" your user by MAC address, there's little you can do....you can't spoof a MAC address that your modem is already using. Otherwise, you'll probably need to run pppoe (as well as iptables rules, a dns resolver, etc) on your linux box. Depending on your ISP you might need either a static IP or run as a dhcp client. BTW, there's nothing stopping your modem from having a local IP address AND running in bridged mode at the same time....I've run my ADSL modem like that for over 15 years, so I can still access it's web interface and query it with snmp. – cas Jun 4 '16 at 2:13
  • BTW, if you do end up with a LAN, I very strongly recommend a dedicated NIC between your modem and your linux router, and another NIC in the linux router for your LAN. – cas Jun 4 '16 at 2:14
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Debian Jessie is more than a year old, and that means Wheezy has been oldstable for more than a year. Unless you have a very good reason you should upgrade.

Typically your box does not need to talk to the modem, it's just there and your box talks to the ISP's equipment. We'll need to know your ISP before we have any chance to answer how to configure your box to do that, but typically (at least from what I've heard/seen) your box should just use DHCP.

Getting your box to talk to your ISP is the same whether is should route traffic from other machines or not.

  • There are some very good reasons for wanting to use a cable/dsl/etc modem as only a dumb bridge - ancient firmware with known (or suspected) security holes or back-doors. Also, some modems only allow configuration by a web interface, which severely restricts what you can do with it. – cas Jun 4 '16 at 2:05
  • I know, I use a cable modem as a bridge myself. - And I don't say otherwise in the answer. – Henrik Jun 5 '16 at 8:42

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