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Airport Express issues when plugged into Ethernet

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Ok, for anyone who is familiar with the AE, I'm scratching my head on this one...


I recently bought and Airport Express. I imagine this may not be limited to Airport Express, though.


I have ethernet run through the house; The Airport Express is connected directly to our cable modem in the upstairs office. One line runs to an ethernet switch in the office, to which two computers are connected.  Everything works fine and Wifi is great.


However... I also have ethernet running down through the wall into the basement, where it goes into another switch, then feeds off to two downstairs rooms.


When I plug the AE into the ethernet plug that does downstairs, suddenly, Wifi no longer works, and I start getting IP conflicts popping up everywhere - including on hard-wired computers, such as the iMac I'm on now... which is set to DHCP.


(This did not happen with my old router.)





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1. Power down the AE.

2. Remove the switch in the basement.

3. Turn off any computer in the basement.

4. Use the Ethernet cable that comes directly from the AE and plug it into any of the basement computers and power on.

5. Power up the AE and report back if the upstairs vs down stairs computer operate with out conflict.


NOTE: Anytime a computer is set to DHCP a predefined IP lease is present. Normally when you reboot a computer the system will obtain the new IP address handed out by the router. Also note if your modem is a *Router / Modem* and you used it before and it was bridged this may also be the root cause.


Your job is to first determine if you have a router / modem and if you do are you using it? If you did use it simply check if the IP ranges are the same and refresh the unit. If your ISP router / modem was not in play here its more likely your basement computers were still using the leased DHCP addresses.


A simple release / renew of the IP address will flush the computer and grab a new DHCP address offered by the AE.

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Hi Teken,


There are no computers connected via cable outside the office.


There are a few things like Apple TV, Playstation, and an IP Camera.


Not sure if this changes anything?


Hello Andrew,


I understood from your initial post that upon plugging in a *wired* Ethernet cable to the down stairs computers you immediately saw a IP conflict.


Is this not correct?


If so its easily solved by first determining what devices have been assigned IP addresses. You can use one of several smart applications like iNet / Fing to determine what IP and devices are on the network. Your router would be the first thing to check though and keep in mind most unmanaged switches need to be power cycled when a new router / modem is installed. 

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There are no computers on the line outside the office, but when I plug in the ethernet cable that leads downstairs (to the switch in the basement), IP conflicts start popping up on the other wired computers in the office as well as on laptops and other devices on WiFi.


I think I've power cycled just about everything...


I have recently replaced another switch on the first floor; however the lights on the basement switch appear to be normal...



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1. Is the ISP modem also a router?

2. Do you use the WiFi / Router function of the modem assuming question one is valid?

3. Have you turned off all WiFi devices and rebooted them one at a time with the new AE in place?


NOTE: As indicated up above please disconnect the switch in the basement and plug in the cable directly into a computer and observe if there is still a IP conflict.

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Disconnect the Ethernet cables from all of the devices in the basement. Verify that your network is now OK.


One by one, REBOOT (or power-cycle) and re-connect each device. Allow sufficient time for trouble to appear.


You probably have one of more devices that have been assigned FIXED IP addresses, and there is a conflict with either another fixed IP address or a DHCP pool address.


Unfortunately, if conflicting with a DHCP pool address, the problem could "go away" for quite some time, and then come back.


Check the configuration of each device. It will take some digging into documentation. See if the device is set to use DHCP, or instead has a fixed IP address assigned. For example, go into "Settings" on the Apple TV, and find your way to the network status page.


Fixed IP addresses are EVIL unless you keep GOOD track of them - AND know what you are doing. But I would never use them, because you can achieve essentially the same thing with a central control point by using DHCP reservations.


Most devices are fine with a DHCP pool address. You only need a fixed address if, for example, you will set your router to forward some Internet port to a device. Then it will have to be at a fixed address. But the best way to achieve a fixed address is to make a DHCP reservation on your router.


I don't see anything in your basement that needs a fixed IP address.



If you followed my instructions (or similar) on your other post about your new router, you should remove the Ethernet 2 interface from your Mac now. (What did UDI tech support have you do to resolve?)


I'm really surprised that you have IP address conflicts, because the new router uses a different subnet than the old one. So, if there were devices with fixed addresses, there wouldn't be any conflict - in fact, you wouldn't be able to reach the devices at all! Did you reconfigure any of these after changing routers?

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Thanks -


Ok - ah... there are no devices in the basement except the switch. I assume I should disconnect the switch and work my way to each individual device from there, checking for trouble as I go.


Also - forgot to add the ISY connected to the Airport Extreme. It's DHCP. In the past, I remember setting it to a static IP - I don't remember why at the time - had something to do with connecting remotely, I think.

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Your diagram shows several devices plugged in in the basement. Xbox, Playstation, Apple TV, etc.


Is your diagram wrong?


It's unlikely the problem is the switch, unless it is a "smart switch" that has a management port.


Switch, or switches? Your diagram shows three - one in the office, feeding one in the basement, and then that one feeding another in the living room.


Accuracy is important. The thing that will cause the trouble will be the thing you didn't tell us about! ;)


I wouldn't bother disconnecting the switches. Disconnect all of the devices from the switches, and check for trouble. Then bring devices back one at a time, rebooting each, checking for trouble, checking device configuration.


If you do not know how to configure a device or view it's configuration, dig in with Google and find out. Set each one to use DHCP.

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What's literally in the basement is irrelevant. Your basement switch feeds a family room switch, and that switch feeds a living room switch. Disconnect everything that the basement switch feeds (the devices in the family room and living room). Bring them back one at a time.

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My bad - it's an Extreme.


Diagram is correct. As noted above, the ISY is currently directly connected to the Airport Extreme, and it works. 


I don't think there are any other devices on the line.


I'll go through 1 by 1, leaving the switches on.



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Basically everything disconnected except the switches.

With basically nothing connected except the switches, when I plug the house ethernet line into the airport, every other computer begins getting IP conflicts.


It appears the Airport continues to assign new addresses, which, in turn, fail, saying something is already using that number.

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Basically everything disconnected except the switches.


With basically nothing connected except the switches, when I plug the house ethernet line into the airport, every other computer begins getting IP conflicts.


It appears the Airport continues to assign new addresses, which, in turn, fail, saying something is already using that number.


1. I'm going to keep this simple - please remove any switch in the network.

2. Unplug the AE router from the ISP modem and power it off.

3. Reboot the ISP modem - wait for it to come back up.

4. Plug the AE router back into the ISP modem and wait for it to retrieve all the network attributes.

5. Have every network device in the entire home disconnected or turned off / unplugged.


- Add one single tethered Ethernet device to the network and confirm it operates. Continue to add other hardwired network devices until completed. Do not add any wireless devices to the network until the first step is done.


Please report back your findings . . .

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So, it has nothing to do with the hardwired devices in the downstairs rooms? That was a false correlation?


I agree with turn off EVERYTHING. BUT... as a practical matter, no DHCP reservation lasts more than 24 hours, and so they would have expired long ago.


It sounds to me like you may have TWO DHCP servers - one on the Airport Extreme, and one on the modem. You should only have one.


Perhaps the previous router did not have DHCP set up? Maybe it was configured for "DHCP pass-through".


I think at this point you need help from your Internet provider.


Do you rent the modem from them, or did you buy the modem?


Does your internet provider include "multiple IP addresses"? Usually this would be something you would pay extra for. And it's something you do not need...


I'm curious what Tekken mean by "tethered" too.


Further explanation: DHCP works like this... a device sends a broadcast message, saying essentially "I need an IP address assigned. My MAC address is: <MAC address>. Any DHCP server, please respond with an address." MAC address is the unique Ethernet (not IP) address of the device. Note that there can be only ONE DHCP server on a physical/logical subnet. The server responds, handing out an IP address. "Here's your address: <IP address>. It will expire after <time period>." The server keeps a "pool" of addresses, keeps track of the correlation between MAC addresses and IP addresses, and avoids handing the same address out twice (unless expired). As a safeguard, though, the server generally will work through the pool from front to back before recycling addresses. AND, since it remembers the correlation between MAC and IP addresses, it will generally assign the same IP address repeatedly to the same device upon "renewal". (The device will ask for renewal once the time period is up.)


OK, now modems have a DHCP server too. In MOST cases, though, it is used ONLY for your router to be assigned an IP address to be used to talk to the modem. It is a physically and logically separate subnet from your house network. There should only be TWO devices on that network - the modem and the router. You should be able to see the details in your router status pages and your modem status pages. (Do you know how to access the modem admin interface? It typically will be at, and will be routed from your network.


I said "in most cases". That's because sometimes the ISP might provide multiple IP addresses. USUALLY when this is done it is in order to provide the household with some small range of fixed IP addresses. (Like 4, or 8, or 16).  So, the modem might continue to hand-out addresses after the first one. Actually, I think most ISPs now will hand-out a small number (like 4) of (not fixed) addresses, as a convenience and to avoid unnecessary service calls. (e.g. when somebody changes a router! - if only one address, then it would fail until the old router's reservation expired...) And can be useful for simple, small networks with no router.


There SHOULDN'T be any way to have both DHCP pass-through AND a DHCP server set-up on a router. But I don't have an Apple router, so can't verify that it's not possible with your router. So, if your router is set up to provide DHCP service (is it?), DHCP requests should go to the router and stop there. (They won't be passed along to the modem.)


What is the "WAN Interface LAN address" shown on the Airport Extreme? It should NOT be in the range 10.0.1.x!

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Anything hardwired is considered a tethered connection.





It's one of those confusing terms with multiple definitions. (Plus we know Tekken likes to write his own dictionary. ;) )


AT&T refers to using a WiFi connection from your notebook computer to your phone to access the Internet as "tethered". Look Ma (Bell), no wires! But, still it's "tethered", I guess because the notebook is dependent on the phone for it's Internet.


With the huge mobile data caps today, BTW, the $10/month for AT&T tethering is a viable and inexpensive backup plan for Internet, and I have it primarily for that purpose. (I don't travel much with a notebook.) I used to have DSL backup.


OK, if you have kids that YouTube and Netflix in the back seat of the MiniVan, maybe "huge data caps" not so much!

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What is the "WAN Interface LAN address" shown on the Airport Extreme? It should NOT be in the range 10.0.1.x!


Before we get too much further - maybe this is the issue; while it's not listed exactly the way you have it, it shows this:


LAN IP Address:



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Oh - also... I realized that although a single Ethernet line runs from the office down into the basement, because of the way everything was wired and bound, there's no way I can tell what cable is what...


I'm going to need to get a tracer to sort things out.



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