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10.6: Avoid a DHCP issue with Dual Band Airport Extreme OS X Server
Snow Leopard only hintWhile playing with Snow Leopard Server's various services, I noticed DHCP wasn't working. Actually, it worked at first for my laptop, then it stopped. Then I noticed the iPhones were not able to receive IPs either. I thought it was something with my server, so I drew a network diagram, and it gave me an idea.

I have an Internet modem connected to a Netgear router, to which the AirPort Extreme (Dual Band) is connected. My Snow Leopard Server machine is connected via the AirPort, as are all other clients. My drawing showed that when my Server was connected on the 5Ghz side, and the DHCP clients were connected on the 2.4Ghz side, DHCP would not work.

I confirmed this by splitting the dual band and connecting server and all clients on the 2.4GHz channel only. Set up this way, DHCP worked great; problem solved! I'm not sure if that makes perfect sense to the IP specialists, but I almost think this is a bug with the Dual Band implementation.

[robg adds: I can't confirm this one, but I'd be interested in comments from others using Server and Dual Band AirPort to see if this is a general issue or not.]
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10.6: Avoid a DHCP issue with Dual Band Airport Extreme | 19 comments | Create New Account
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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: stwaldo on Mar 18, '10 08:34:33AM

I've had issues using the dual-band feature as well, but I haven't been able to diagnose it to a DHCP issue, although that may explain it. Using 10.6.2, my iPhone, and some other appliances (a Tivo and Xbox 360, both on wireless). While I have the iMacs on the 5 GHz network and have no issue, my iPhone regularly fails to connect to the 2.4GHz. When it has issues connecting, it will either "see" the network but refuse to connect, or cannot see the network at all. Either way, about 5 minutes later it will connect after all.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: Alemany on Mar 18, '10 08:56:09AM

Hmmm.. I dont have this issue. I have an iMac and a MacPro connected to 5ghz, and a playstation a BB and 2 iPHones connected to the 2.4, and a separate guest account where a Dell from a contractor connects regulalry and I have not seen these issues.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: madh on Mar 21, '10 08:48:58AM

So is it your Mac Pro that is running OSX DHCP Server? PS3 can get a DHCP IP from that server on the other band?



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: digs0 on Mar 18, '10 10:44:45AM

Interesting observation. I haven't been able to test yet, but I wonder if this is my problem as well. I don't have the extra router in my case, though, and I'm all Apple. My setup is a dual-band Time Capsule with separate network names (as required, I think?) for the 5 GHz and 2.4 GHz band. I also occasionally have a guest network active as well. There's an Airport Express extending the network. I find that often my MBP loses its internet connection (even though it claims to be connected to the 5GHz network and my hardwired iMac still accesses the net fine), and the iPhones will also often drop their connections. In my case, I'm wondering if somehow the laptop is accessing the network via the Express, but the Express has lost the connection to the Time Capsule, and that's causing the problem. It's all very confusing to me, but the issue has become all too frequent. I've also mainly noticed it since having the motherboard replaced on the MBP-- but I think that's just a coincidence.

---
DJR



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: ab on Mar 18, '10 12:10:42PM

This same issue occurs on my Dual Band Airport Extreme network about once every 30 - 45 days. In order to resolve the issue I must reboot the Airport Extreme router. The router is connected directly to my DSL modem, serves DHCP, and routes all traffic for the network. I previously had an XBOX360 with the USB wireless N adapter connected to this network. With that configuration the loss of DHCP services from the Airport Extreme would occur about every 2 - 3 days and seemed to happen when the XBOX was used or just after. I separated the bands into 2 distinct WiFi network names, but there is still a bug in the router that causes the DHCP service to die after some trigger I cannot exactly identify. An AppleTV is the only 5ghz user device I have. I tried to resolve this by adding 2 Airport Express station to serve as bridges only for Ethernet switches. Several devices now only connect to the WiFi network via the Airport Express routers ethernet ports. The Airport Express devices only connect to the 5ghz network to bridge the data. This configuration is more stable (less frequent loss of DHCP services) but did not fix the issue completely. Router logs do not provide me with any clue as to why or when the crash occurred because it continues to route for all previous DHCP clients, it just stops giving addresses for new ones. I can confirm no max number of WiFi clients is being exceeded. Seems it is time I send a bug report to Apple for this issue.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: BrentT on Mar 19, '10 08:04:50AM

I can confirm having the same issue. Only a hard router reboot will get my 2.4 ghz band to connect to a Mac Pro Dual G5. Every 30 to 45 days seems to be the same timeframe for me.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: axcess99 on Mar 18, '10 04:36:26PM

First i'll preface this with that I don't have a dual-band configured base station. But it sounds like he has two different wifi-networks in parallel (a supported feature of the dual-band base stations).

Can any of the devices on the 2.4ghz network connect to any of the devices on the 5ghz band? If not, then it seems like he has it configured with a guest network (which is supposed to create two networks isolated from one another, including services like DHCP).



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: madh on Mar 21, '10 08:59:29AM

Yes, I have my airport set in the mode where it appears as one SSID but Apple devices can choose the 2.4 or 5 ghz band depending on which is decided to be better. Up until I started playing with OSX Server services all clients in my network regardless of actual band they were connected to worked fine. I started working with DNS and DHCP on the OSX server, turned off these services on my Netgear FVS338. DNS worked fine, you could ping anything on the network. The only issue was that the OSX DHCP Server would not issue IP's to any device on the opposite Band. The client would end up getting that default IP 169.?.?.?, can't remember the exact IP. It seems to be something specifically related to the way DHCP requests are made. It would be interesting to have another DHCP server to test thats its not just OSX DHCP. May have to pull one of my Windows Servers out of retirement.



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To madh...
Authored by: leamanc on Mar 18, '10 07:06:34PM

Can you tell me what purpose the Netgear router serves in your network? I could see a need for it if you wanted some extra wired ports, but you say that all clients (and even the server) is connected via WiFi on the AirPort base station.

I might me missing something here, but for the life of me, I can't think of it.

And I don't know if this is a home setup, or for a small office or what, but wouldn't you want your server to have a hard-wired connection? I just wouldn't want my server to depend on WiFi; I'd want to make sure it was getting maximum I/O, and WiFi speeds are so variable.



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To madh...
Authored by: madh on Mar 18, '10 08:09:53PM

Absolutely not the right setup. It is a home network, I bought a Mac Mini Server to learn its capabilities as I come from the Windows IT world. My current house is not wired at all. I had to make due.
Wanted to post this in case anyone else was experiencing the same problem.

I have managed to run one wire across my basement and up to the Mac Mini. It is now connected directly to my Netgear as it should be. This also allowed my to set the airport back to auto 2.4/5 ghz mode under one SSID.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: luomat on Mar 18, '10 08:21:24PM

My guess is that both the Netgear and the Airport were both trying to hand out DHCP addresses, and one of the "won" and the other "lost".

If the Netgear is setup to send out DHCP addresses, the Airport needs to be put into "Bridge mode".

That said, I'm not sure why the Netgear is there at all. Do you need more Ethernet ports than the Airport has to offer?



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: cawaker on Mar 19, '10 01:54:59PM

I agree thats what it sounds like. be sure the netgear isnt doign my dhcp serving if you want the airport to handle it with the wifi clients.

also I second the others, whats the need for the netgear router at all? if you need it for wired ports, be sure its not doing any routing or dhcp. turn off any nat or firewall.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: madh on Mar 21, '10 08:46:28AM

Very first thing I did once bringing my Snow Leopard DHCP & DNS server online was to disable DHCP & DNS on my Netgear FVS338. I even rebooted just in case.

Edited on Mar 21, '10 09:11:21AM by madh



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: emaven on Mar 18, '10 11:14:07PM

I'm using a time capsule. My 2 17" MacBook pros C2D are connected with ethernet cables. My 15"MacBook pro CD is connected via i-fi. They are all on the same 5GHz network. I also have a guest network on the 2.4GHz.

I notice quite often that the wireless connection seems to drop, even though airport is on and the signal is strong. When I check with Network Diagnostics, the first 3 buttons are green, but the ISP button is red. Eventually, the button turns green and the connection is made. I thought there might be a problem with the Mac, but as it is out of warranty, and the problem is intermittent, I have not pursued the problem.

I am going to use the other Macs wirelessly, and see if the problem occurs with them as well.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: madh on Mar 21, '10 09:02:23AM

I realize you bought the 5ghz to use it, but maybe try forcing everything to the 2.4 ghz band just until you prove whether it fixes the problem. That way you'll know whether its related to the two bands or not.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: eusebe on Mar 19, '10 08:33:15AM

I have got a similar issue with a Time Capsule. The problem I got is that I couldn't route between devices connected at 5Ghz and devices connected at 2,4GHz. Both worked well to access the Internet but could not see each other. That doesn't happen on regular basis, but only after a certain period of running. Rebooting the TC always fixes the issue for a limited period.
I called Apple and they replaced my TC by a new one which has not this issue since several weeks.



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: imageworx on Mar 22, '10 06:17:13AM

This may be unrelated, but I had installed the dual band Airport Extreme for a client and was frustrated with the Apple Admin software. It is not clear that setting up a guest network and the 5ghz network would cause such an issue. Since I was short on time, I took it out and put in a DLink DIR-655 and the macs were happy (Dlink seems to be the only router that just works with macs and pcs).
I also noticed you have a Netgear firewall/router. Is this a home setup? Seems rather overkill unless you are running a server accessed from outside?

---
To BeOS or Not to BeOS



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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: hengelr on Apr 21, '10 02:30:16AM
I bought a Macbook Pro 13" two weeks ago. I already had an iBook (g), PS3 (g) and PSP (g) connected over wifi to a dual band Airport Extreme. (I also have the latest model iMac and a HD wired to the AE). I use the setting WPA/WPA2 and 802.11n / g compatible. This results in one 'tranmitter' in the AE using WPA and 802.11g and the other WPA2 and 802.11n. Both having the same airport network name. After a 2 days the MacBook started to have problems obtaining an IP adres after opening the lid. I think the problem is that somtimes it tries to connect to the n network (requiring an WPA2 key) and sometimes to the g network (requiring an WPA key). Is there a way to force the MacBook in always using the n network?

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10.6: Avoid a DHCP issue with Dual Band Airport Extreme
Authored by: milk269 on Aug 03, '10 12:03:14AM

i have the os 9.2 ... how do i change chennals. and or upgrade to the wireless web?



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