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You are here: MacNN Forums > Enthusiast Zone > Networking > Using the same static IP address on both ethernet & airport network setting

Using the same static IP address on both ethernet & airport network setting
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m021478
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Jun 12, 2009, 02:14 AM
 
I am trying to maintain the same LAN IP address on my Macbook regardless of whether I am connected via ethernet or airport, and I've had issues in the past simply configuring the IPv4 address manually for each (and setting them both to the same static IP).

I'd like to be able to do this without resorting to static IP or futzing with Locations by performing the following steps:

• Setting the same DHCP Client ID on my laptop for both the Ethernet interface as well as the Airport interface.
• Then set up a DHCP Reservation in the Airport Utilities configuration for that Client ID.
• Then make sure that the Ethernet is above the Airport on the Network control panel in System Preferences.

Only problem is my expertise in with (relatively) advance network configuration is extremely minimal, and I was hoping someone might be able to provide me wtih a simply step by step walk-through of how to accomplish this task.

Any suggestions would be greatly appreciated... Thanks!
     
turtle777
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Jun 12, 2009, 02:20 AM
 
I don't understand.

What where your problems with manual IP addresses ?

I have never dealt with Client IDs, but alas, I have never had problems with manual IPs either.

-t
     
ghporter
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Jun 12, 2009, 10:30 AM
 
I'm curious why you want to maintain the same LAN IP. Depending on your hardware, forcing two different client devices (your Ethernet port and your AirPort card) to use the same IP can cause some issues. TCP/IP standards have the router associate the client device's Media Access Control address with a single IP address; having two different devices with the same IP is the definition of an IP conflict. (For purists, an AirPort ID is not identical to a MAC address, but it is FUNCTIONALLY the same thing.)

Further, controlling the order that connections are made does NOT prevent your AirPort card from connecting, even though you already have a wired connection. I'm currently looking at my AirPort indicator, and it shows I have a great signal from my wireless network and I'm connected through it, though I leave my iMac plugged in for faster performance on my 100BaseT wired network. (I keep AirPort enabled so I can monitor my wireless network.)

Glenn -----OTR/L, MOT, Tx
     
turtle777
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Jun 12, 2009, 11:30 AM
 
Good points, Glenn.

-t
     
Camelot
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Jun 13, 2009, 02:32 PM
 
It's entirely possible to configure both interfaces with the same IP address if you really need. It's just that you can't have both interfaces active at the same time.

Therefore your best solution is to create two Locations in System Preferences -> Network.

For one location, e.g. 'wired', disable the AirPort interface completely and manually configure the wired ethernet port with the address you want.
For the other location, e.g. 'wireless', disable the wired interface and configure the wireless interface.

Now you have both interfaces configured with the same address and you can use the Apple -> Location menu to switch between them.
Gods don't kill people - people with Gods kill people.
     
m021478  (op)
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Jun 13, 2009, 06:31 PM
 
Originally Posted by ghporter View Post
I'm curious why you want to maintain the same LAN IP. Depending on your hardware, forcing two different client devices (your Ethernet port and your AirPort card) to use the same IP can cause some issues.
I think you are missing my point here... I am not trying to be connected via both ethernet and airport at the same time using the same static IP address...

I've set the service order of my connections so that if my ethernet cable is plugged in, then my ethernet connection takes priority and it assumes a static IP address that I've designated for use with my Macbook Pro (meaning that I've forwarded ports on my router to the static IP of my Macbook pro so that I can use applications like Transmission, etc, etc... and then, once the ethernet cable gets unplugged and I carry my laptop into another room in my apartment where I will use the Macbook's airport connection, then airport connection assumes the same static IP address that my ethernet had previously been using... this way, when using any of the dozens of application that require a port be forwarded to a predetermined static ip, I don't have to manually switch to a new 'Location in the Network Preference Pane, but rather the switch will be made automatically...

Hope that helps clarify...
     
Cold Warrior
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Jun 13, 2009, 06:46 PM
 
System Prefs > Network.
Airport > Advanced > TCP/IP > input dhcp client id
Ethernet > Advanced > TCP/IP > input dhcp client id

Airport Utility > Internet > DHCP > add your reservation based off of client id.
     
ghporter
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Jun 13, 2009, 06:52 PM
 
Originally Posted by m021478 View Post
I think you are missing my point here... I am not trying to be connected via both ethernet and airport at the same time using the same static IP address...
That was not the way I'd read your post. Obviously you not only have a good reason for maintaining the same IP for both connections, you know how to prevent them from being concurrent. I'd worried about this, since it is the kind of thing that an inexperienced user with just a little information might say. Clearly this is not the case.

I'd have gone the easy router and just used different locations... But then I don't use the same sorts of apps you do.

Glenn -----OTR/L, MOT, Tx
     
Cold Warrior
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Jun 14, 2009, 10:19 AM
 
By the way, an alternative would be to add an airport express to your network. Just plug it in to the ethernet line where you'd normally plug in your macbook, then configure the Express for bridged mode. Now you can reserve an IP based off of MAC address, and your macbook will use wifi signals wherever you go in your apartment.
     
   
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