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Fri, Jun 21, 2019 2:48 AM

Internet stops working when ethernet cable connected to gateway

I have the following setup and every time I connect the 3rd ethernet cable both WiFi and hardwired Internet stops working.


Setup: I have an AT&T gateway modem (WiFi through this is disabled). Plugged into the gateway is a ethernet cable to my Netgear router. Second ethernet cable going to security system.


Issue: everything works just fine until I plug into the gateway a third ethernet cable that goes to a switch in another room - from that switch I connect to a DVD player, directv box and VoIP adapter. When I plug this in, there is a visible WiFi network but it won’t let me connect and/or disconnects me and any hardwire cable stops working too.


When I remove the 3rd ethernet cable plugged in the internet will start working within a few minutes.


i can’t figure it out and not sure what I should even try


See quick diagram for reference.



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125K Messages

a year ago

HI @Manderson55,


We will be happy to help!

Since both the Internet Gateway and the IP Passthrough host use the same IP address, new sessions that conflict with existing sessions will be rejected by the BGW210. For example, suppose you are working from home using an IPSec tunnel from the router and from the IP Passthrough host.  In this case, the first one to start the IPSec traffic will be allowed; the second one from the WAN is indistinguishable and will fail.  Please view this article on how to Configure IP Passthrough and DMZ. 

Hope this helps!

Lafayette, AT&T Community Specialist

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