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I have a ADSL2+ modem (with 4 lan and an access point)(lets name it "D") which is connected to internet and 2 pc connected to it via wireless adapters, I connected a 4 lan switch(lets name it "S") via a cable to one of "D"'s lan port and connected 3 more pc to the "S" via cable, I can ping all my computers on network and they are all visible but I have no internet connection, when I unplug the cable (the one from "D" to "S") I can access the internet, what should I do?

D is a D-Link 2640U
S is a TP-LINK TL-WR542G

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Clarify just a little bit, are you saying that when you plug the switch into the modem (S-D) then the modem will no longer connect to the internet? So the wireless computers, the 3 on the switch, and the modem are all disconnected from the internet, but every computer can ping every other computer? – Dennis Jan 5 at 12:00
D is still connected to internet but no other computer has access to internet – JJOkacha Jan 5 at 12:03
When D and S are connect, can you ping the gateway from the clients connected via wire or wireless? The wireless clients also have no internet when you connect S with D? – Robert Jan 5 at 12:24
Not an answer, just an opinion. It sounds like all you are trying to do is connect 3 wired computers in one place to a wireless modem/router in another. Using a second wireless router seems like overkill to me. Why not just use a basic inexpensive un-managed 5 or 8 port switch rather than another router? – Dennis Jan 5 at 15:54
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2 Answers

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There are a lot of possible causes for your problem but I would first try to check:

  • S is connected to a LAN port in D FROM (on S) a LAN port, not WAN

  • you have only 1 DHCP active (D or S - D would be easier as it would automatically send the right default gateway to clients) (usually default setting for switches is to have DHCP on and should be off on one of them)

  • DNS relay working on D (and off on S if using only 1 network with 1 dhcp)

  • default gateway on S = D IP

  • default gateway on all machines (supplied by DHCP) = D IP

  • all machines are in same network (only 4th IP block is different) (not necessary but easier to configure not needing additional routes)

  • if you are using fixed IP, be sure to have them in same network and setting default gateways and DNS to D

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up vote 1 down vote

The TL-WR542G is a normal wireless broadband router so it most likely has DHCP enabled by default. On top of that, it is possible the IP pool is in the same default range as the D-Link 2640U. So, disable DHCP on "S" in order to allow "D" to assign IP addresses to the computers connected through "S". Otherwise, the routers will fight over being in control.

Screen Shot

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