Airport Extreme DHCP Reservations Help

Welcome to the discussion area, Stefan!

For example, I reserved 10.0.1.5 for my MacBook, which might be already taken by another machine previously connected. Why is the Extreme not "reserving" this address? Am I missing something?

As you guessed, another device has probably already been assigned this IP address previously. It will keep this for 24 Hours from the time of the lease, unless you've changed the lease time. If you entered the MAC address correctly, your MacBook will get 10.0.1.5 when the lease renews.

But, keep in mind your Mac has an AirPort ID for wireless and an Ethernet ID for ethernet connections. So, if you entered the Ethernet ID and expect for your Mac connected via wireless to get 10.0.1.5, it won't. You'll have to matchup the AirPort ID on your Mac if you want the wireless to get 10.0.1.5 on the next go around.

Some have Client IDs, but most are blank. Is there and easy (reliable) way to find out what each device is (or at least any more info)? I seem to have more devices connected than I own, although my wireless network is hidden and password protected.

If you've been mucking around in the DHCP area and restarting your AirPort Extreme things may look pretty disorganized at the moment. Leave things alone for 24 hours and things will look more logical. Some things won't even appear until they renew again within 24 hours. This is normal.

As I mentioned above, all of your Macs have both an AirPort ID and and Ethernet ID so a single Mac can look like 2 different devices if you've been using both wireless and ethernet.

Try this on one of your Macs:

Open System Preferences
Open Network
Click on AirPort
Click Advanced at the lower right
Click the TCP/IP tab
Type in the name that you want to appear in the DHCP Client ID area. +MacBook Pro Wireless+, for example
Click OK, then click Apply

On the same Mac, open System Preferences again
Open Network
Click on Ethernet
Click Advanced
Click the TCP/IP tab
Type in the name that you want to appear for Ethernet
Click OK, then Apply

Do the same for all of your Macs running Leopard or Snow Leopard

If you have an iPhone, you'll need to touch Settings, then Wi-Fi, touch on the small arrow to the right of your wireless network name, touch the DHCP tab and type in the name you want to appear under Client ID.

The iPad is probably similar. I don't have one, so can't say for sure on that.

I have a NAS box sitting in my network, which is requesting a static IP from the Extreme (so I can always access it with a specific IP address). However, I don't ever see it appearing in the "DHCP Clients" list. I would love to also set up a DHCP reservation for that device, but I don't know its MAC address.

The MAC address is on a label on the back or bottom of the device. If it's on the network, it's getting an IP address. Maybe you can figure out which MAC address belongs to the NAS by process of elimination if you name all of your Macs and iPhones, etc.

Message was edited by: Bob Timmons

I set up several DHCP address reservations in the "Internet > DHCP" tab. Those work well most of the time, except when an address is already taken. For example, I reserved 10.0.1.5 for my MacBook, which might be already taken by another machine previously connected. Why is the Extreme not "reserving" this address? Am I missing something?

As you know, you can create DHCP reservations by either MAC address or DHCP Client ID. It is possible that you may have an existing DHCP client on the network that is still using a previously assigned IP address that may temporarily conflict with a reservation. By default, the 802.11n AirPort Extreme Base Station (AEBSn) DHCP Server provides leased IP addresses for a 24-hour period.

You can force any client to request a new DHCP lease via System Preferences > Network > AirPort or Ethernet depending on your connection type > Advanced > TCP/IP > Renew DHCP Lease

Note: On the same window, notice this is where you can enter a DHCP Client ID for your Mac.

Under the "DHCP Clients" tab, I see all (?) the devices connected to the Extreme (both wirelessly and wired), along with their IP addresses and MAC addresses. Some have Client IDs, but most are blank. Is there and easy (reliable) way to find out what each device is (or at least any more info)? I seem to have more devices connected than I own, although my wireless network is hidden and password protected.

Entering the DHCP Client IDs for all of your Macs will go a little way to help distinguish what devices are connected. Other IPs can be network printers, NAS devices, or other routers on your network.

I have a NAS box sitting in my network, which is requesting a static IP from the Extreme (so I can always access it with a specific IP address). However, I don't ever see it appearing in the "DHCP Clients" list.

If the NAS box is configured with a static IP address, then it is not performing as a DHCP client, and most likely, why it's not showing up in the DHCP Clients list.

I would love to also set up a DHCP reservation for that device, but I don't know its MAC address, since it is not showing in that list.

Usually, the MAC address of the NAS would be printed on a label, but if not then you could ascertain the address by using the Terminal on your Mac.

o Run Terminal (located in the \Applications\Utilities folder)
o At the prompt, enter arp -a, and then press Return.

You should now see a list of IP addresses and their associated MAC addresses. Since you know the NAS' IP address, you should be able to find its associated MAC address from the list.

I was hoping that "reserving" means to keep a specific IP only for the use of a specific MAC address and otherwise never assign it.I was hoping that "reserving" means to keep a specific IP only for the use of a specific MAC address and otherwise never assign it.

That's exactly what it does. For example, I've assigned my network printer an IP address of say, 10.0.1.20 and entered in the MAC address of the device along with a description, "Network Printer" into the DHCP Reservation box. The printer has been receiving the IP address I specified ever since I set up the "reservation". No other device ever gets that address.

Now, if you are setting up a reservation for a given device, say your main desktop and you assign it 10.0.1.5 and enter the MAC address, etc....but, that 10.0.1.5 address is already in use, you'll have to wait for the lease on the device to run out in the next 24 hours, then the desktop gets the 10.0.1.5 address at that time.

When you "reserve" an IP address for a given device based on its MAC address, the IP address you specify will always be assigned to that device.

If after the next 24 hours or so, you see that's not happening, then that's another issue. You'll need to go back in to your DHCP Reservation List and double check the MAC address, etc. I suppose it's possible that the DHCP service is not functioning correctly, but I can't ever remember seeing a post in that regard here on the forum boards.

I have 2 computer on my Airport Extreme network I am controlling with my Macbook pro (ARD Admin)
G5 Tower - on ethernet, Macbook Air wireless (which travels outside network sometimes)

When inside the network I can control both computers... no problem.
When outside I can control only the G5.

I have setup a DHCP Reservation for the G5 on the Airport Utility so I can access it from outside. Works great... I can add a second DHCP Reservation for the Macbook Air but the Port Mapping does not allow a second mapping to the Air.

How can I do this?

Second question - DHCP Reservation - If the Airport remaps the DHCP addresses each 24 hours, Can i use an IP over the range... say - 205? This way the target computer will always be available?