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I have a device which doesn't have an option to pick up an IP address via DHCP.

If I configure my DHCP server to give a specific IP to the MAC address of that device (effectively reserving that address for the device), can I safely connect it to the network or will the DHCP server have a problem with this configuration?

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up vote 2 down vote accepted

The dhcp does not check what IP addresses are active on the network at starting time, therefore your setup will run fine.

You are probably thinking of the case when your IP is already present on the network at the time of dhcp startup but the dhcp server only checks that at the time of request from a client.

Even then, the server would refuse to offer that IP to other mac address than yours and yours will never ask for it, anyway.

So yes, you can safely connect it the way you described

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Just as I hoped - cheers! – Jon Cage Jul 2 '13 at 9:31
I did once encounter a router that refused to route traffic to an IP address assigned a statically to a MAC address unless that MAC address has a valid reservation for the IP. But that is very unusual. Still, I recommend using IP addresses outside the router's DHCP range for static IP addresses. – David Schwartz Jul 2 '13 at 9:59
@Jon Cage, what exactly do you mean by "a device which doesn't have an option to pick up an IP address via DHCP"? – packets Jul 2 '13 at 10:11
@Costin Gusa, while I agree that a device with a statically assigned IP address will not make an IP request, the device could cause a conflict if this address is not outside the DHCP server's assignable IP range or within a reserved IP range. Example: Let's say the device in question is offline when the server meets another computer request and assigns the address which is configured on the device, later when the device connects to the LAN, you're right, the DCHP server won't have a problem with the address conflict, but both machines with the same IP will have issues... – packets Jul 2 '13 at 10:11
@packets there is no assumption, as the OP has stated about making a reservation. so it's either black or white, except for the corner-case David Schwartz mentioned. If another device will want to abuse the first device, it can do it regardless of dhcp server settings. the OP only wants to make sure statically assigning an ip plus dhcp reservation won't hurt his dhcp server. – Costin Gușă Jul 2 '13 at 11:17

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