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Not a networking guy by trade, but I know enough to get myself into some trouble. And I think I've managed it. I need to set up a DHCP server on a PC for a small subnet of 3 or 4 devices. I have the DHCP server set up and working in one configuration, but not another. I define the configurations and give more background below.

I have a small network of devices, 3 plus a "smart" managed switch and a PC, and I'd like to have the PC serve as the DHCP server. The DHCP configuration works on another rig where the situation is similar (buncha devices, a switch, and a PC with 2 NICs), except that there the managed switch is full featured, and about 20 times more expensive than the little Netgear ProSafe GS105 I'm using. And that seems to be my problem. The DHCP server expects a Default Gateway for the network, and it won't work if I point it back at itself (in this case .100). So I took the switch, gave it .1 as the address and it wants a default gateway as well. I give it .100 and the DHCP server .1, with the intent that all the devices will forward to .1 and then the switch will forward to .100. But that doesn't work, either. I don't get any errors that I'm aware of, but the DHCP Discover messages never make it to the PC.

The thing is, it's a new requirement that this network runs with DHCP enabled (sort of... there's a lot of background there, so let's just take that as a given for now), so I'm trying to do this in a cost-effective way. Is there some reason a "smart" switch can't function as a default gateway? Or am I missing something else more fundamental?

I'm using OpenDHCP to configure the DHCP on the PC. In it, I have a range set with the subnet set to 255.255.255.0 and the default gateway set to the address of my switch (.1/13). The NIC is set to the address of the PC (.100/26). It works in the second case but not in the first. So it seems like this is only an issue when I'm using the smaller switch. Is there somewhere else I should look for problems?
I noticed that on my larger switch the default gateway is blank. I can't do that on the smaller switch.

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The default gateway is the gateway/router towards the Internet (or the largest part of your network). You can't just use anything that doesn't even route.

You need to set the DHCP server to hand out your Internet router's IP as default gateway.

A switch doesn't forward traffic based on IP addresses unless it's a layer-3 switch and routing is enabled. Also, it can't be the default gateway unless it's an L3 switch and it's got a default route towards the Internet itself.

Note that host configurations (like the DHCP setup) and consumer-grade devices (like the GS105) are explicitly off-topic here.

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