# Is this possible: connecting 2 ethernet cables to modem's single ethernet port?



## Lord Vader

On my modem, which is one of the newer and faster ones, it has the traditional single ethernet port into which my router's ethernet cable goes. My router is maxed out with its ports all used.

Just curious as to whether it's possible to take my modem's one ethernet port and connect two ethernet cables into it via a multi-port switch--kind of like a phone jack splitter allowing two phone lines to go into one phone port, except here we have a modem's single ethernet port. 

Now, I know such ethernet ports and all work differently from phone jacks, so we don't use splitters, per se, but you get the picture.

I'm curious as to whether I can do this because I was thinking of running one, specific device right into my modem with my router being the other device connected; hence the desire to have a switch/splitter of some sort.


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## Davenlr

Never tried it, but I suspect unless your modem has a built in switch, it wont work. You would have two devices trying to use one IP address. Why not just get a cheap multiport switch and run it off a port on your router?


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## P Smith

Each Ethernet port designed for one target port (device or another port).
*
No exceptions !*

Find new switch (those are chip now - Fry's have it for $5-10 on sale sometimes)


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## Lord Vader

P Smith said:


> Each Ethernet port designed for one target port (device or another port).


That would seem to make sense.

So how do multi-port switches get away with this?

BTW, I have an 8-port switch in my living room, to which are connected 3 HD DVRs, my A/V receiver, Blu-Ray player, and one other device. This runs directly to one port on my router.


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## Lord Vader

Davenlr said:



> You would have two devices trying to use one IP address.


Isn't this what the numerous other devices connected via the router are doing?


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## Davenlr

No, the router assigns a different IP address to each device plugged into its switch.


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## Lord Vader

Duh!


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## Stewart Vernon

It depends.

IF your end-device (the one with the single port that you want to use) is a router that can route traffic, then the answer is yes. Most switches have a mode that supports daisy-chaining other switches off of a single port.

But... if the device is designed with just a single-use port... then the answer would be no.

So it depends on the device capabilities AND how it is currently configured.

The easier way, though, is to attach another switch to your existing switch. I would be surprised if you switch doesn't have a port on it that can be used to daisy-chain... though you might have to flip a switch/button on that port OR configure the port via firmware.


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## davidjplatt

All you have to do is get a 5 port or 8 port switch (even a gigabit switch with 5 ports can be had for $20 or an 8 port switch for $30), unplug one of teh devices currently plugged into the router, plug the switch in there and then plug the device you removed into the switch. Then you have 3 additional ports (or 6 additional if you use an 8 port switch) to use. Just like you are doing in the other room.


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## Lord Vader

I kinda figured that's the way I'd have to go. It's really not that critical, though, as everything is thus far working fine. It was more of a "can I do this if possible?" type of scenario.


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## davidjplatt

Stewart Vernon said:


> It depends.
> The easier way, though, is to attach another switch to your existing switch. I would be surprised if you switch doesn't have a port on it that can be used to daisy-chain... though you might have to flip a switch/button on that port OR configure the port via firmware.


Any port on a switch can be used to "daisy-chain" another switch off of it. Many years ago ports used to be one type and a crossover cable had to be used or a switch flipped. I haven't seen a new switch being made that isn't auto-sensing. It knows whether a DCE or DTE is connected to it (DCE=Data Communication Equipment, DTE=Data Terminal Equipment).


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## SayWhat?

Just daisy-chain as many as you want.

Modem to router.
One router port out to a switch, use the other three router ports for PCs if you wish or connect each router port to a switch.


Note that each port on a switch is dual use, input/output. There usually is not a dedicated uplink port on consumer devices, so in daisy chaining, you use two ports of each switch in the chain and only one port in the last switch.

1 Input
2 Output to next switch
3 PC
4 PC
5 PC


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## Lord Vader

I guess my only concern, and it was a mild one at that, was if there would be any kind of degradation on the signal for any devices connected via a switch. Let's say, for example, I wanted to connect my VoIP service directly to the modem but couldn't because one can only connect one device--a router. My VoIP adapter is connected through my router already; I was curious as to whether connecting it or anything else to a switch that then goes to the router would cause any kind of degradation.


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## P Smith

No degradation - each switch/router reconditions output signals, max cable length is 300'.


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## SayWhat?

300*"*, as in inches ? Um, no; 100 meters, or about 330 feet.

That's the point of the switch though is to effectively share the WAN connection as well as LAN devices.


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## Stewart Vernon

davidjplatt said:


> Any port on a switch can be used to "daisy-chain" another switch off of it. Many years ago ports used to be one type and a crossover cable had to be used or a switch flipped. I haven't seen a new switch being made that isn't auto-sensing. It knows whether a DCE or DTE is connected to it (DCE=Data Communication Equipment, DTE=Data Terminal Equipment).


Like I said... I said he "might" have to flip a switch or something. I don't know what kind of switch he has. IF he has a newer one, then you're right... it will plug-and-play and just work... but I still have some old ones where I do have to push a button... so I didn't want to tell him to just do it, then find out he has an older switch that doesn't work that way.


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