Possible to connect a wireless adsl modem router to an existing adsl modem?

Dumb question, but I've got sudden IT brain fade for some reason.

I've moved into a new apartment in a far, far away country.

The apartment has internet via a basic old wired modem (a ZTE 831) with a single LAN port. I wanted to replace it with a nice new wireless router (D-Link DSL-2640U), BUT...

... the new router cannot be configured because there is no way of finding out who the ISP is, let alone what the username, password or other account settings might be.

(The apartment is not registered to any of the main ISPs, so the internet might be spliced in from another account, and the details all since lost. Situation entirely normal for this part of the world....)

Hence I was wondering if its possible to simply run the single LAN port from the existing modem into the DSL port of the new D-Link, and whether the D-Link would then simply act as a switch and deliver the signal via its 4 LAN ports and the wifi?

I'm asking for the simple reason that if I plug it in to "see what happens" and it somehow fnucks up the existing logon, I'll really be up poo creek without a paddle.
If your router is a cable router (i.e. with no modem built-in), the answer is yes, connect the LAN port of the existing router to the uplink port of your router. It will work, and won't mess anything up. This has the advantage that no-one can easily "look" into your network. Should be fine.
What old Nis said above... Bear in mind though that the old router LAN connection needs to go into the uplink Ethernet connection on the new one (as ON said), not the DSL port (as you suggested). Presumably the new one is also a wifi AP, and will do that for you as well?
Have you tried to login to the user interface on the ZTE 831?

IP address to login is "deault gateway" ip revealed when you (in XP)

Start, Run, cmd, ipconfig /all

Enter address in browser (eg default username: admin password: admin

What other two said is correct, connect the LAN ouput from the ZTE to the WAN port on the DLink
Have you tried to login to the user interface on the ZTE 831?

IP address to login is "deault gateway" ip revealed when you (in XP)

Start, Run, cmd, ipconfig /all

Enter address in browser (eg default username: admin password: admin

What other two said is correct, connect the LAN ouput from the ZTE to the WAN port on the DLink

O.k., logged onto the ZTE831 and pulled off all the data I could see; the only account data appeared to be "user".

I then disconnected the ZTE831 and attempted to set up the D-Link, using its installation CD and set-up wizard. This time the wizard appeared to identify a local ISP, and accepted the user/user logon. The wizard indicated that the D-Link had correctly set up. Unfortunately there was no internet connection. Logging onto the router didn't reveal any account settings that might allow a log-on to the ISP.

I then reconnected the ZTE831 and connected its single LAN port to one of the four LAN ports on the D-Link. The D-Link automatically recognised this as a private Ethernet line, and passed the signal to the other three LAN ports and the WiFi.

The WiFi works, and can be picked up and connected/logged-on by wireless devices (tablet, another laptop), Unfortunately, although these devices are logged on and see a strong signal, there is no data traffic. As the D-Link is still at its default settings, there are no apparent firewall filters that might be blocking wireless traffic.

A further complication is that - of course - both routers share the same logon IP address and "admin" password. Logon attempts cause the ZTE to come up; the D-Link can only be accessed by first disconnecting the ZTE. I tried to change the IP address on the D-Link, but for some reason the address always reverts straight back again.

At this point I reach the limit of my router daisy-chaining abilities!

Any ideas what might be preventing traffic across the wifi?
Hmm, this one could be a bit tricky.
I suspect you're being served a single IP address where the subnet mask is such that you don't have an IP range, if you get my cack handed explanation.
I'm making a few guesses here but I think you're going to need another cable modem, from this you can connect up the wireless router and use it as a dumb wireless access point. But, the tricky bit is configuring the port on the cable modem which would then use Static Address Translation to route any traffic (say from address in to the IP that you are being served on the cable modem.
I'll be honest it's a terrible easy thing to setup so think it would need a decent Sysadmin who knows their onions and can think out of the box.
Good luck

The fact that they both have the same ip address is the problem, you need to change your new router ip range to a different subnet ie same subnet mask and this should help, make sure the DHCP server range is also changed as they sometimes are edited separately

If there are no obvious username/password details on the ZTE the local telco/isp may be autenticating using the ZTE's MAC like Virgin Cable do in UK. Alternatively, as with O2 UK there may be No username/password combo and the ISP assumes if the line has their ADSAL on it then that's OK and any modem may be used.

So try connecting the D-Link with no name/pwd after canging it's MAC to the MAC of the ZTE.

As for daisy-chaining the ZTE through D-Link's ethernet port, it may be possible, but difficult. You realy need a router not a modem/router for that.

You could try making the lan port connected to the modem a dmz, turn off DHCP and give each device a static local IP. I think OMJT is suggesting similar.
I'll just add a bit more address IP addresses.
If your cable modem in being given an IP Address from a DHCP server then you may have an address like with a subnet mask of Now, the subnet mask is the tricky bit, with a subnet mask of it means that all IP addresses from to are valid and can communicate. BUT, if you have a subnet mask of then that will only give you a range of to
I have seen cable modems that give you a single IP address and the subnet mask is such that you cannot add any more IP numbers to the range.
That's why I've suggested the Static Address Translation route.
Of course, I could be widely off the mark here and it might be as simple as making 2 static IP address for the modems.
I'd recommend someone with a bit of knowledge to come and have a look at it to be honest, I may be over complicating it.

Good info, didn't know the vs DHCP IP allocation.

OP 4(T),

Are you on cable or pstn/copper/bt-equivalent?

Any progress?
Hi all,

No success with getting data traffic over the wifi connection.

Tried to use the ZTE MAC in the D-Link, but got nowhere trying to get the D-Link authenticated onto the provider's line (its via phone line, not cable).

Have gone back to the ZTE only for the time being. Looks like we may have identified the provider, so will try and contact them to get some configuration details.

Thanks for the contributions. I'll have to get a copy of "Routers for Dummies" or similar in order to expand my limited knowledge!
surely you need to access your wireless modem/router and turn it into a repeater, thus disabling the modem portion, as one already exists (ie the wired one).

I use a wired modem with a tp-link repeater, i think you are after a similar setup?

Configure your wlan as an access point

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