I have a static IP and I wanted to set up another one. After calling up my ISP and getting another static address, I tried to plug a second router into my NetVanta 838T modem, but could not connect to the internet. I tried the new router in the first plug and it worked, so I think the settings are correct.

I called up my ISP and they told me it was not possible to do this with the hardware I have. Is this true, and if so, what is the purpose of having 4 ethernet ports on that modem?

Edit: Added in a switch between the routers and the modem and it accomplishes what we wanted, but I still don't understand the purpose of the extra ethernet ports on the modem. Before


closed as off-topic by kasperd, Esa Jokinen, Paul Haldane, Tom O'Connor, MadHatter May 19 '17 at 7:22

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    I assume the piece of hardware that you have is a Modem / Router combo, probably offered by your telco. If it is a combo device, then the modem aspect is not actually exposed to you, the end user, but is instead hard wired to the 4 port switch available on the case. – Matt Clark Apr 12 '17 at 2:24

The ethernet ports are for connecting multiple devices within your LOCAL network so they can communicate with each other. The modem, assumingly, from your ISP provides ROUTING functions to the ISP from your network but only on the specific port that's allowed to do that.

The other ethernet ports would allow you to plug in say a PC, laptop and printer and them be all on the same subnet and be able to "talk" to each other. Basically it becomes a "dumb" switch for you to have a local network without having an additional switch.


Straight from the NetVanta documentation:

The NetVanta 838T is a Carrier Ethernet Network Termination Unit (NTU) that terminates up to eight e.SHDSL copper pairs. Four 10/100 Ethernet ports are provided for customer use.

So to reiterate what I said, they are for creating a LOCAL network (LAN) as opposed to adding an additional switch.

  • We put another switch in between the modem and the original router and it actually does what we originally wanted. Now we have two separate routers with different static, global ip addresses. I guess my original question still stands, though what is the purpose of those additional ports, if they are not acting like a switch? If I plugged in a computer into one of those ports would it attach to my local network? If so, which one? – horriblyUnpythonic Apr 12 '17 at 17:20
  • @horriblyUnpythonic They should be acting like a switch. What you're reporting is very strange. Could you explain in more detail precisely how router 2 doesn't work? Does the port light come on? (It might be an MDI/MDIX conflict.) – David Schwartz Apr 13 '17 at 1:01
  • It did come on, when I plugged in the second router, but the router didn't connect to the internet. It did work when router 2 was connected to the first port. Router 1 stopped working when plugged into any other port, although I didn't explicitly try various combinations of ports and the order in which they were connected. I thought it might be an MDI/MDIX thing (after finding out what that meant), but the doc here says that the ports should be 'auto sensing' and 'auto MDI/MDIX'. portal.adtran.com/pub/Library/Data_Sheets/Default_Public/… – horriblyUnpythonic Apr 13 '17 at 17:46

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