Need advice on properly setting up network hardware.  (DSL Modem --> Router -->Switches)

Posted on 2008-10-14
Last Modified: 2010-04-21

I need some help to solve a mysterious network problem.

Here's our setup:

DSL Modem supplied by the phone company (SIEMENS SPEEDSTREAM 6520)
Connected to:
D-Link router (DI-604UP)
Connected to:
2 D-Link switches (DES-1024D and DSS-8+)
All devices connect to one of these two switches.
The Modem has been configured with all the DSL login credentials.

The Problem:

Users have sporadic internet connectivity.  They can revive their connections by using the Windows networking "repair" function, but this only works briefly.
Rebooting the modem also works (briefly)
The LAN (managed by the D-Link router) seems to work fine in spite of the Internet connectivity issue.
If I connect a laptop directly to the modem, Internet connectivity is not a problem.
Modem IP range is 192.168.2.*, Router IP range is 192.168.0.*
Note: Since the modem has been configured with all the DSL login credentials.  I have left the router with its default "Dynamic IP" setting for the WAN port. I have tried to configure it with the PPPOE credentials (as part of my troubleshooting), but I couldn't get that to work.

If you need any additional details, please don't hesitate to ask!

Many thanks for your input.

Question by:lmgregg
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LVL 13

Accepted Solution

CrashDummy_MS earned 380 total points
ID: 22715361
It sounds like you have some double NATing going on. Your DSL modem is acting as a router, and your router is also acting as a router, traffic to the internet gets NATed twice and leads to weird things happening.

Log into your DSL modem's config page and set it to bridged mode. Then on your DSL router set it to PPPOE and put in your DSL login and password there.

Assisted Solution

JanSchotsmans earned 120 total points
ID: 22715386
Considering direct to modem and lan connectivity is no problem, its more then likely the router is a problem.

Most of these cheapo DSL/Cable routers hang and lock periodicly, especially if you ask them to route traffic for multiple PC's/Devices.

Check if you can find any firmware updates for the router in question, firmware updates usually help a bit with instability.

Best thing to do though is get a decent router (and decent modem or a decent combo of the 2).
ISP supplied modems are, except in cases of Bussines/Professional installations, utter crap and any router under 100$ is usually crap too.

If you want stability and plenty of power to route for multiple clients, check out the Cisco 8xx series DSL/Cable modem/router combo's or something in the range of a Linksys rv082

Expert Comment

ID: 22715419
Double natting could be the problem too indeed, but if the Siemens is configured as a router and not a bridge, then there really is no point in having the D-Link router around in the first place.
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LVL 13

Expert Comment

ID: 22715534
Good point on not really needing the D-Link, Jan. It probably has more configuration options/abilities than the router part of the Siemens modem, but the Siemens probably still will do everything they need.

Try removing the D-Link from the network Imgregg. Connect the DSL modem directly to one of the switches and see how that goes.

Author Comment

ID: 22715569
More info:  The router was installed only recently (two weeks ago) because the modem was failing quite frequently and killing the LAN (LAN uptime is more important because we run some networked applications that don't crash gracefully).

So, two weeks ago, I bought and installed the router between the modem and the switches.  The LAN has been stable since then.
Early last week, I installed a replacement modem from the phone company.

This double NATing thing sounds like it is worth exploring.  Configuring the SpeedStream 6520 as a bridge isn't an option on their user-interface.  

Question - Can I buy any DSL modem and use it?  Or do I have to use the modem provided by our ISP?

Expert Comment

ID: 22715655
If you have the pppoe credentials from your ISP, you can just swap it out with another modem, fill in the pppoe login and get going.

If you have a bussines running behind that setup, its really worth exploring and investing in a  8xx series Cisco.

Cisco 827 ADSL you can find heaps of them even on e-Bay if your on a budget.
LVL 13

Expert Comment

ID: 22715667
Ah, well knowing that, then I'd tend to think that the modem needs replacing, but you may try updating to latest firmware first. It's worth a shot.

You should be safe just buying a new DSL modem. They generally aren't ISP specific. The ones the ISP gives out are probably configured to be ISP specific, but if you go out and buy one it won't be that way.

Expert Comment

ID: 22715698
The Cisco Small Business 106 and 107 series are pritty good value for money too btw.

Also, be sure to see which line you have incomming, ISDN or POTS, the 106 and 826 are POTS, 107 and 827 are ISDN.

Author Comment

ID: 22717577

Is this the Cisco826 you are recommending?  Is it a router/dsl modem combo?

Expert Comment

ID: 22718476
Its a Cisco Lab for CCNA training model. Dunno if you can actually use those things as a production system. (I skipped all the Cisco Elitist training crap and figured it out for myself instead :p)

But since I see these models persistently way cheaper then the normal version I'm betting they are rigged in a way so you can't use them in a production environment.

But even so, would you trust buying something lower then 1/10th its true value on ebay?

Author Comment

ID: 22725674
I (think) I have everything up and running okay now.

Here are the details.

To run the Siemens Speedstream 6520 as a bridge, you need to paperclip reset it, then just leave it as is (don't provide any account info in the setup).  This is not easy information to find online, so I figured I should mention it.

The problem appears to have been a second D-Link DI-604 router I was using as a switch at the far end of our building to allow two devices to use the same network connection.  I removed it, and all our problems seem to have gone away.  Kind of weird because it seemed to be doing its job as a switch quite well.  We have another router hooked up as a switch for the same reason in another room and it is working without issue.

Still - I plan to invest in some better hardware.  I appreciate your help and advice.  Must run to get the kids, I'll assign points tonight.


Author Closing Comment

ID: 31506053
Extremely helpful advice.  I really appreciate your help

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