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TOPIC: DHCP Will This work?

DHCP Will This work? 11 years 9 months ago #7295

  • tsunami
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Hi Guys, i have a question regarding using a single switch for 2 DHCP servers.
The Topology actually is like this.

we have a 16 port D-LINK switch and an 8 port HUB. we also have a D-LINK airplus wireless accesspoint with in built routing, nating and DHCP functions.
The internet connectivity is taken from a cable modem and the address assignment is DHCP from the provider.

wright now, the WAN interface of the Access Point (AP) is connected to the 8 port HUB. The cable modem's ethernet interface is also connected to the HUB. The LAN interface of the AP is connected to the 16 port switch. Here all the PCs for accessing are connected. The AP is configured with DHCP so that it provides the IP addresses in the network 192.168.0.0 to the PCs connected to the swicth.

My question is can i connect the cable modem's ethenet interface and the WAN interface of the router to the switch too.
will this work as there are 2 DHCP distributors in the same broadcast domain?

note:- The DHCP IP from the provider is registered to MAC addres of the WAN interface of the AP.

thanks for the reply
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Re: DHCP Will This work? 11 years 9 months ago #7302

First of all, no. Having 2 dhcp servers on one physical segment is almost certain to cause problems. You'd probably be able to get it to work some of the time, probably depending upon the order in which you turned stuff on, but it's still a bad idea.

HOWEVER...

what else is connected to that 8 port hub? If all that's connected is your modem and your AP, then it's completely extraneous. All you need to connect the two devices is a straight through cable, which is probably what you've got going from your Hub to your AP and modem anyways, though I suppose they could be crossover, and possibly still work. If your cables aren't physically long enough, then you could probably head to a local computer shop and get them to make one for you for a much better price than you'll find at Best Buy or RadioShack or any other electronics stores. As long as the total length of the cable is less than 100 meters (that's 328 feet), you've absolutely no reason to be using a hub there.

It's also possible that you need a crossover cable between the modem and the AP, but that's less common, and varies by modem manufacturer.

A quick way to check a cable is to hold both ends of the cable next to eachother, and look at the connectors the same way (i.e. bottom of both, or top of both) and look at the color of the wires... if they look the same, it's straightthrough, if some of the wires are switched, it's a crossover.
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