How do I split my modem connection into a router and an additional ethernet output?

Question

I have my cable modem in one room. I have a ethernet wire going through the wall connecting to the router. I have an Office I want to run an ethernet cable to, which would be pretty easy to do if I can run the wire to the room w/ the cable modem. Unfortunately I can't run a wire from my router to the Office.

Is this possible with a splitter or switch or some other device?

Hopefully the image helps:

Solution 1

The easiest option will be to move the router to where the modem is and put a switch where the router was by your TV and use the existing cable between the current modem and router setup to connect the router and switch. Then you can run a cable from the office to your router. If WiFi will be an issue with the change, you can add a wireless access point to your switch as well. If you add a access point, have the name and security settings be the same as your router.

Solution 2

All cable modems in my experience will, on the user-accessible Ethernet-port side, only talk to the first device that connects to it or that responds to it. They will ignore all other devices until a reboot.

So even if you physically connect more than one device to the Ethernet port of a cable modem, which is possible if you use an Ethernet switch, it won't work.

FYI most routers have a built in Ethernet switch with ports labeled LAN 1,2,3,4. Some cable modems have built in routers and 4-port switches.

You can do this:

• Move existing router next to cable modem (call this the first router).
• Disable wireless on this router.
• Obtain a second router and configure like so:
  • Connect nothing to second router's WAN port.
  • Assign router IP in same subnet as first router, with an IP that won't get affected by first router's DHCP range.
  • Connect LAN port of first router to LAN port of second router.
  • Disable DHCP on second router.
  • Disable routing on this second router (you want only the wireless) if this is possible.
  • Configure wireless as you like on second router.
  • If you have wired devices near where you want the wireless to originate from, you can still connect them to the LAN ports of the second router, and it will work.

I have a similar setup, the "second router" in my case is an Asus RT-AC56U (256MB dual core unit with a big heatsink over the chipset, running OpenWRT derivative) which has a convenient "Access Point" setting that didn't require messing with a lot of settings after the fact. Any router with wireless that can be configured above should work though.

Comments

[David Schwartz]

Why disable wireless on the first router?

[David Schwartz]

You can also use a second router as a combination switch and access point. Just don't use its WAN port and disable its DHCP server. Assign it an IP address inside the main router's LAN IP block but outside its DHCP range.

[HazardousGlitch]

Of course. I was going the easiest route with the least amount of configuration needed.

[joel]

OK, thanks. My only question is how would I add a wireless access point to the switch? Do you have a hardware recommendation for a wireless access point? The extender is OK but it's kind of annoying having to switch to the _EXT connection

[David Schwartz]

Do not use a wireless extender. Just use either an access point or a second router acting as a switch and access point. You can use pretty much any router with the choice depending on your budget, port requirements, and WiFi requirements. For example, an Archer C50 (my first hit googling "cheap dual band router") is about $40 and would give you dual band WiFi and three wired ports (because you can't use the WAN port and need to use one port to connect to the main router).

[HazardousGlitch]

I'm not sure what you mean by _EXT connection.

[joel]

Thanks @DavidSchwartz. Just to clarify: Cable modem > cheap router. Cheap wire w/ a wired connection to office and the "nicer" router in the central location?

[David Schwartz]

@joel The downside of that is that your "cheap router" will be doing all the routing. If you want to do port forwarding, firewalling, or anything like that, it'd be the "cheap router" you'd have to configure it in and that would have to do the work. Make sure the router connected to the modem has enough horsepower and a suitable UI for your routing needs. The router connected to the wired devices is just acting as a switch and access point. It needs good WiFi though. You can use the WiFi in both routers for better coverage and give them the same SSID and key (ideally different channels).

[David Schwartz]

@joel Make sure to disable the DHCP server in the second router. And do not use its WAN port (unless it supports an option to re-assign the WAN port as an additional LAN port). Assign it a LAN IP address inside the first router's LAN address block but outside its DHCP range. So if the first router is 192.168.1.1/24 and the DHCP range is .100 to .200, 192.168.1.2 is a good choice for the second router.

[HazardousGlitch]

I think your comments are worthy of an answer @DavidSchwartz

[Mazura]

It took me a second: you're talking about a passive splitter - I've never even seen one of those.

[LawrenceC]

Passive splitting is only possible on ancient thicknet/thinnet network cables of the 80's. It still wouldn't work in this scenario.

[LawrenceC]

Per disabling the wireless, it will likely work OK if SSIDs are the same, but eliminate that as a potential problem source during setup.

[Mazura]

That's a great solution : switch back to BNC :)