Trouble Connecting a Router to a Router

To get an extra port to the cable modem, I tried hooking up an unused DSL Modem/Router, but this caused one PC to lose internet connection.

The ORIGINAL LAN diagram (Figure 1) shows our working home configuration. The Trendnet router had 4 ports, all being used. We had a PS3 unit which we would swap in and out with another PC.

Then I found an unused DSL Router Modem - a Westell VersaLink Model 327W
           (actually, Model: D90-327W15-06 Rev.D)

I removed the telephone cord, and plugged it in (possibly using wrong ports and/or cables) as shown in Figure 2. All seemed to work for a few hours awhile with some intermittent problems.

Then the Windows 7 PC (on SWITCH1) reported that there was no internet connection. WV1 (Windows Vista), XP1, XP2 were all connected OK).

I removed the power from the Westell unit, and the Windows 7 PC regained connection almost immediately.

I was surprised that only the Windows 7 PC lost connection. Can the Westell DSL Router Modem be used essentially as a switch to give us the extra port that we need? Any idea why just one PC was affected by the configuration in Figure 2?

I can get a switch, but would think that I should be able to hook up the DSL unit to give us the extra port. All the cables in my home are of the same type.


Here is a manual I found online for the Westell unit.

From the manual, it appears that the IP address is (

 Cable Modem
Router-Gateway ( Trendnet TWG-BRF114
  ^                     ^        ^       ^
  |                      |         |        |
-SWITCH1-     WV1    XP1    XP2
^     ^    ^    
|      |     |
XB  W7 XP3

All the cables I have are the same.


 Cable Modem
Router-Gateway (
  ^                    ^       ^          ^
  |                     |        |           |
-SWITCH1-    WV1   XP1    DSL_Router_Modem (DSL not used)
^      ^    ^                            ^        ^
 |      |     |                             |         |
XB  W7  XP3                        XP2     PS3


Thanks for your assistance.

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To use a router as a switch you have to go into the router's web interface and disable DHCP on the LAN. Make it the sam network as the other routher
Use a patch cable from a lan port to a lan port from the primary router to the second. It will now be a switch.

JohnBusiness Consultant (Owner)Commented:
In the "unused" Router, first turn off DHCP in this router, and then when you hook it up, use only the switch connections, not the WAN connections. Log into the router and give it a static IP address from the Trendnet router (that is, an IP outside the DHCP range of the Trendnet). ... Thinkpads_User
JohnBusiness Consultant (Owner)Commented:
I think that is pretty much what I wrote above.   ... Thinkpads_User
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phoffricAuthor Commented:
>> an IP outside the DHCP range of the Trendnet
How do I determine the DHCP range  of the Trendnet?

>> Use a patch cable
The cables I have now connect a PC to the Trendnet router, or PC to a switch. This same cable is being used to connect SWITCH1 to the Trendnet router. For the two routers that I have, do I have to get a different cable?
phoffricAuthor Commented:
Thanks for the replies.

BTW - I was wondering why it sort of worked for most of the PCs, but in the end (not initially), just the Windows 7 PC lost its internet connection.
"why it sort of worked for most of the PCs, but in the end (not initially), just the Windows 7 PC lost its internet connection"
If you have 2 devices handing out IP addresses (DHCP) in your network it is a very unpredictable situation.  
It is probable that the Windows 7 PC acquired an address from the new router or acquired the same address as the router depending on how connected.
As stated above - turn off DHCP in the newly introduced router and use only the switch ports not the WAN port of the new router.  The WAN or Internet port will be empty.  It is not joining two separate networks you are just using it for its' switch.  You should give it an IP address outside of the DHCP range of your original router.  So if your original router is and it is handing out thru you will want to use something above 50 and use the as the gateway.  This will allow you to have a known address to get into your new router.  I often do this with wireless routers to use them as an access point.
JohnBusiness Consultant (Owner)Commented:
>>> How do I determine the DHCP range  of the Trendnet?

Open the management interface on the Trendnet (Normally or some variant), go the DHCP settings and observe the range for DHCP (normally - 200). A static IP on the Trendnet can be (for example).

>>> For the two routers that I have, do I have to get a different cable?

No, assuming the cables are regular cables.  If you made them yourself, you might wish to switch to pre-made cables.

>>>  I was wondering why it sort of worked for most of the PCs, but in the end (not initially)

Having two sources of DHCP is deadly and problem Windows 7 got confused (it has new networking stuff inside).

... Thinkpads_User
phoffricAuthor Commented:
Hey, thanks for all your input. I'll be attending to this but yesterday I got an unknown RAID 0 error. I'm working this now.
phoffricAuthor Commented:
Thanks all for your guidance. No problems for a day. Much obliged.

http:#34125887 & http:#34125889 (2 minutes apart): explains to disable DHCP in the router that is to be converted to a switch; and change IP address of this router to be, where y is outside the range of the Gateway Router (Trendnet).

http:#34125889 identifies the cable to use between the two routers

http:#34127076 explains why disabling DHCP is necessary to prevent conflicts

http:#34127103 clarifies how to determine the DHCP range  of the Trendnet and clarifies the types of cable to use
JohnBusiness Consultant (Owner)Commented:
Thank you. I was pleased to assist.  .... Thinkpads_User
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