DHCP on OS X Server with an Airport Extreme on the network!

Just turn off the 'Distribute IP addresses' option in AirPort Admin. This will disable the DHCP server built into the AirPort Extreme and leave the server as the only device on the network issuing DHCP addresses.

It should be AirPort Admin -> (base station) -> Internet -> Internet connection.

You should have a 'Connection Sharing' pop-up menu with options that include 'Share a public IP address', 'Distribute a range of IP addresses' and 'Off (bridge mode)'.

From your earlier post it sounds like you're in 'Distribute a range of IP addresses' mode. Change this to 'Share a public IP address' and you're set.

if I set it to "off (bridge mode)" will the server then handle DHCP?

Yes.

if I set it to "off (bridge mode)" will the server then handle DHCP?

No. Or, at least, not in the way you want.

If you turn the base station into bridge mode then you disable the whole NAT setup on the router - it just becomes a dumb bridge between the wired and wireless networks. This means that the public IP address handed out by your ISP will be injected into your network, and the DHCP clients on your private LAN won't be able to get out to the internet.

I don't have that specific model of base station, but I'm 99% sure there's the option to turn off the DHCP server while maintaining the NAT mode. Are there no other options there that look likely?

Mulle wrote:
it is set to share a public ip address, and when in this mode the Airport handles DHCP, witch i don't want...

if I set it to "off (bridge mode)" will the server then handle DHCP?

I do have one of the same model of Airport Extreme, and having checked mine there are three relevant choices.

Bridge Mode - The Airport does not act as the DHCP Server but also does not do NAT
Share a public address - The Airport does do NAT but also does DHCP
Distribute a range of IP Addresses - The Airport does not do NAT but does do DHCP

Unfortunately it does not appear to have a choice which lets it do NAT but not DHCP.

However I have not seen anything in your post that explains why letting the Airport continue to be the DHCP Server is no longer suitable for you, so one option would be to leave things as they are.

My recommendation would be to have the ZyXEL do the NAT and you can have the DHCP function turned off in the ZyXEL, and have the Airport connected to the same LAN as the (LAN side of the) ZyXEL and the Server. The Airport should configured to be in Bridging Mode (which means it does not do DHCP) and then you can happily and safely have the Mac OS X Server be your DHCP Server.

A simplified network diagram would be

Server--------+---(LAN)-------ZyXEL--->ADSL
 |
 Airport Extreme

I have a suspicion you were previously having both the Airport and the ZyXEL do NAT (this is called double NAT) and this is unnecessary.

Unfortunately it does not appear to have a choice which lets it do NAT but not DHCP.

Yes you do. That's the 'Share a public IP address' option.

'Share a public IP' = NAT
'Distribute a range of IP addresses' = NAT w/ DHCP

Camelot wrote:

Unfortunately it does not appear to have a choice which lets it do NAT but not DHCP.

Yes you do. That's the 'Share a public IP address' option.

'Share a public IP' = NAT
'Distribute a range of IP addresses' = NAT w/ DHCP

When you select "Share a public IP" it still shows the DHCP Server tab and this seems to make it clear it also acts as a DHCP Server in that mode. The DHCP tab has no off button and it is auto-filled with valid details. If your Airport does not show the DHCP tab (or has an off button) when in Share a public IP address mode, then you must have a different model. I have checked three models and all show DHCP in Share a public IP address mode.

AirPort Extreme 802.11n - Fast Ethernet (7.5.2 firmware)
AirPort Extreme 802.11n - Gigabit Ethernet (7.5.2 firmware)
AirPort Extreme - Simultaneous Dual Band (7.5.2 firmware)

The only mode that does not show a DHCP tab is Bridge mode, and hence Bridge mode is the only mode that it does not act as a DHCP Server.

(Slight correction, an AirPort Extreme base-station configured to extend a Wireless network, i.e. is the extender and not the master, also disables the DHCP server on the extender which makes sense as an extender is de-facto in Bridge mode.)

Therefore 'Share a public IP' = NAT with DHCP
'Distribute a range of IP addresses' = DHCP without NAT
(and Bridge = no NAT and no DHCP)

I therefore maintain that the only configuration that will meet the original posters requirements is as per my previous post.

What you may be being confused about is that the ancient Airport Admin Utility for the equally ancient round shaped AirPort base-stations does have the ability to disable the DHCP server however (if you still have it) you can see even then when you disable the DHCP server it clearly says "Internet sharing using network address translation and DHCP is not enabled. Client computers on the network must configure TCP/IP manually. The base station will act as a bridge between the AirPort and the local Ethernet network." in other words even on this old model you still cannot have NAT without DHCP on an AirPort base-station.

There is a workaround I have used, set the DHCP on the Airport to start at a specific IP of your choice and end at the same IP. For example 192.168.1.2 start and end. Then you can set the DHCP reservations tab to a fake mac address like 00:11:22:33:44:55 and set it for 192.168.1.2 or whatever you chose before. Then your Airport has no chance of distributing that IP and then let the server do the DHCP starting at 192.168.1.3 or one more than what you chose for the base station.

It is not pretty, but without that option to turn off DHCP, I don't think it can be done.

HTH,
JL

My Airport extreme is in bridge mode as well...but clients are renewing dhcp no problem....so my question is where am I getting dhcp from (if it's offin bridge mode) and how do I determine exactly what dhcp server is giving me addresses? I also want to set up a mac mini server to dole out addresses.

[Here is how to fetch the DHCP server address|http://labs.hoffmanlabs.com/node/1494].

At its simplest, launch Terminal.app on the DHCP client and issue a sequence similar to the following:

$ ifconfig -l
lo0 gif0 stf0 en0 fw0 en1
$ ipconfig getpacket en0
$ ipconfig getpacket en1
... some stuff ... 
server_identifier (ip): 10.11.12.13
... more stuff ...
$

In the above example, the first device wasn't active (and returned no data) while the second did, and within that data, the IP address 10.11.12.13 is the address of the DHCP server that served up the IP address for this DHCP client.

Mulle wrote:
no the zyxel is not doing NAT , it acts only as an gateway. no DHCP and no NAT from that...
the zyxel is "splitting up my connection to IPTV VoIP and internet for computers. from its ethernet ports.

I cannot get in to the zyxel and changes its configuration, it's preconfigured from my ISP and have tried everything I can find on the web that details how to get access to it.

the thing with only having the Airport extreme do DHCP to one fake client does not work, all my wireless devices dos not get an IP address form the DHCP server, but all wired devices do.

I have a couple of ZyXEL routers but they were not supplied by an ISP so I could configure them. You might be able to do a factory reset but that might lose settings needed for use with your ISP or maybe they have a custom firmware which would reload the same locked down settings. An option would be to buy your own router (the choice I made).

However here is another approach you could consider. Connect the Mac OS X Server (only) directly to the ZyXEL, configure the Mac OS X Server to do NAT (add the NAT service) and share the Internet connection, connect the AirPort Extreme (in Bridge mode) to a second Ethernet port on the Mac OS X Server. Configure Mac OS X Server to do DHCP Server only on this second port.

A Mac Pro or XServe have two built-in Ethernet ports making this easy. If you are using an iMac or Mac mini, then get Apple's USB Ethernet adaptor and use that for linking to the ZyXEL, the Internet speed is not going to strain the USB connection and it keeps the built-in Gigabit port for your LAN. Drivers for the USB Ethernet adapter can be downloaded from http://www.sustworks.com/site/newsusbethernet.html

The above approach makes your Mac OS X Server in to a NAT router.

Your network diagram would then look like

Mac OS X Server Ethernet1--------(NAT)-------------ZyXEL
Mac OS X Server Ethernet2---------LAN--------AirPort Extreme