Internet Service Providers forum


Why Gateway Address ?

by ramusson / February 23, 2015 3:03 PM PST

Hello to all.

I have a ADSL Broadband service where the telephone line terminates on a Modem. The Modem LAN port (there are 4 of them) has a default address as My computer is connected to one of the LAN ports and I have some knowledge on IP address, Mask, Gateway, DHCP, ...

The issue:

I have another modem that has a VOIP interface with a VXS port. In addition to configuring the VOIP interface to the VOIP service provider, this unit needs to be configured to link to the Broadband modem. I find that there are 2 parameters that are a must - DNS address and a Gateway address. The Gateway address puzzles me. Unless I give the correct Gateway address, the VOIP service is a no go.
There is a VOIP service provider - "MagicJack" who offers an unit that interfaces with the Broadband Modem without any hitch - just like in a PC where a connection can be made without entering a Gateway address. Even if I change the Modem IP address, it still connects. What's the trick?

My question. Is it possible to connect a Router to the Modem without defining the Gateway IP address?
Intention: Configure the spare VOIP modem to provide the VOIP service on ANY internet connection without re configuration.

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All Answers

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by R. Proffitt Forum moderator / February 24, 2015 3:11 AM PST
In reply to: Why Gateway Address ?

As to your intention, IP networking is not always zero configuration. There are many instances we must configure the settings.

Some folk maintain that IP ( ) wasn't that great an idea for everyone out there. But it was paid for and free to use so that's how we got here.

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by ramusson / February 25, 2015 3:09 PM PST
In reply to: No.

Yes, as far as I know, Gateway address is a must.
How does Windows PC connect to the Modem without a Gateway address? How does the "MagicJack" connect without a Gateway Address?

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by R. Proffitt Forum moderator / February 26, 2015 3:56 AM PST
In reply to: MagicJack

I use an ethernet cable. As the that magicjack, doesn't it connect to my PC in the USB slot?

I'm taking your question literally here. That is, you lead with asking how to avoid configuration so there's that. But trying to write all that one would have to learn about IP in this small box won't fit. So I'll have to just keep it simple.

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the newest MJ Plus
by James Denison / February 26, 2015 4:42 AM PST
In reply to: Connect?

connect direct to a LAN port. They first must be plugged to USB to setup the new account, but never again after that. They can however be used on LAN or USB, user's choice. It's my home phone system. I use it connected to my house wiring and a 4 phone DECT6 system, the USB port is connected to transformed wall power, and the LAN port to the router. The device itself automatically requests a DHCP assigned IP address from the router when on the LAN port.

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I didn't read a Plus here.
by R. Proffitt Forum moderator / February 26, 2015 4:54 AM PST
In reply to: the newest MJ Plus

But it's a nice thing. I got the feeling the OP wanted more plug and play. For IP networks that's a dream.

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VOIP modem
by James Denison / February 26, 2015 5:03 AM PST
In reply to: Why Gateway Address ?
"My question. Is it possible to connect a Router to the Modem without defining the Gateway IP address?
Intention: Configure the spare VOIP modem to provide the VOIP service on ANY internet connection without re configuration."

This is where I'm confused. A modem is different than a router, although some are modem/routers. We'd need to know what VOIP "modem" you were using to be sure. If it's a modem/router, then the WAN on the VOIP could be connected to a LAN port on the first modem/router. A modem demodulates, so you don't need to demodulate the signal twice. The second maybe configured as a "bridge" as in "daisy chained" to the first one, but it MUST be behind the first one, unless you had it also registered with your ISP and used two assigned IP addresses, which won't happen in the usual home setup. Home setup, everything must go first to the approved registered modem, all else happens behind it.
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by ramusson / February 27, 2015 1:09 PM PST
In reply to: VOIP modem

May be the terms used is confusing.
The "Modem" refers to a ADSL Modem + WiFi Router. I used this term to separate it from another unit which is used as a Router.

The Modem can be of various makes - Dlink, Teracom, TPLink, NetGear, .....All that's common is that the Router of this Modem has an address (can be changed), mask

The VOIP unit (which I refer to as a Router) is a Teracom T2-B-Gawv1.4U10Y-BI. This is a ADSL Modem + Wifi Router with a VOIP interface which has been configured for "CallCentric". (The ADSL part has been disabled and the VOIP packets are routed on "IPLAN").

This point I'm making is that this VOIP unit works ONLY if a Gateway is defined in the unit - in this case
But the "MagicJack" works whether I connect it to the VOIP unit or the "Modem" without any configuration change - like connecting a PC without defining IP addresses, Mask, Gateway, ...

I would like to know how is the connectivity established in such a case. Is it possible to configure the VOIP unit to permit a similar "zero config" connectivity?


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Since DHCP hands out a Gateway.
by R. Proffitt Forum moderator / February 28, 2015 1:12 AM PST
In reply to: details

That's as close to zero config as we get today.

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Well .....
by ramusson / March 10, 2015 4:16 PM PDT

I guess that about sums it up. Active DHCP in the "Modem" allows Internet Access from the VOIP unit, but not VOIP. Guess I got to play around a little. Thanks to all for the input.

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