Which network adapter is being used?

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Level 1

14 points

Which network adapter is being used?

I have three Macs connected in a small office LAN through an Airport Extreme / Time Capsule. They are all with OS Mavericks.

Each Mac is configured both wirelessly and with Ethernet to the Airport Extreme / Time Capsule. They each have two private IP addresses, one for the Wi-Fi adapter and one or the Ethernet adapter. Most of the time, both adapters are simultaneously active on each machine.

I would like to know if it is possible to figure out precisely through which of the adapters is the traffic flowing in some cases. For instance, when I transfer a large file (150 GB) between two computers and I can't seem to be sure it is going through Ethernet or Wi-Fi.

I sometimes diasble WI-FI to ensure traffic is routed through Ethernet but I was hoping that there was a more clean solution to figure out which adapter is doing what at a given time.

Can I figure this out through the Activity Monitor or Terminal?

mac book pro, Mac OS X (10.6.5)

Posted on Dec 16, 2013 2:15 AM

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Answer 1

Barney-15E

Level 10

122,306 points

Dec 16, 2013 3:54 AM in response to lanceloz

The Internet traffic will run through the service that is topmost in the list that has an internet connection.

You can set the service order from the Gear menu at the bottom of the list in the Network System Preferences.

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Answer 2

lanceloz Author

Level 1

14 points

Dec 16, 2013 6:50 AM in response to Barney-15E

Thank you Barney-15E for the response. I did not know about setting the service order.

However, suppose that I started a large file transfer through WI-FI because I was not connected to Ethernet. At this point, I know for sure it is WI-FI because Ethernet adapter is not active.

Then, half way in the file transfer, I plug my Ethernet cable because I arrived at my desk.

Will the file transfer switch seamlessly through the Ethernet adapter now that both are available and that Ethernet has a higher rank in my service order? Will it continue the transfer on the adapter it started with? If I pause and resume would it swap to Ethernet?

I was hoping there was an empirical way to determine what adapter is used at a given moment.

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Answer 3

BobHarris

Level 9

56,939 points

Dec 17, 2013 6:12 AM in response to lanceloz

Then, half way in the file transfer, I plug my Ethernet cable because I arrived at my desk.

I'm not sure the transfer would switch if the IP address is different for the Ethernet vs the WiFi interface. I have not actually tested that.

What I have personally done many times is to arrange for the Ethernet and WiFi interfaces to have the same IP address assigned. Either by having a System Preferences -> Network -> Location with identical fixed IP addresses for Ethernet and WiFi, or what I've done more recently is to give my Etherent and WiFi interfaces the same "DHCP Client ID", and then configure my Airport Extreme to always assigned the same IP address to this DHCP Client ID, which insures that while at Home, my Mac will always have the same IP address for Ethernet and WiFi.

Now if I switch between Ethernet and WiFi, the existing TCP/IP connection associated with the IP address will be able to move between networking interfaces without breaking the TCP/IP connection on that IP address.

Using the same IP address I've tested on my Macs again and again since I got my first WiFi base station back in 2001.

You should verify that plugging/unplugging Ethernet does switch your transfer. Start a large transfer, monitor the transfer speed with something like MenuMeters or iStat Menu, then switch the interface and check to see if the transfer speed matches the current interface, then switch again, and again check the transfer speed.

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Answer 4

lanceloz Author

Level 1

14 points

Dec 17, 2013 2:53 PM in response to BobHarris

This looks like a good idea BobHarris. I am curious to try this. I was hoping though there was an easy way to find out this type of information by looking at the network tab of the Activity Monitor or something equivalent.

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Answer 5

BobHarris

Level 9

56,939 points

Dec 17, 2013 3:46 PM in response to lanceloz

System Preferences -> Network

Select the interface on the left

If the IP address is not displayed after selecting the interface, click on "Advanced" -> TCP/IP and you will see your IP address.

Or from a Terminal session:

ifconfig

en0 should be your Ethernet interface, and en1 should be your WiFi interface.

I've found the MenuMeters Network menu bar feature will also show the IP address for your interfaces.

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Answer 6

Barney-15E

Level 10

122,306 points

Dec 16, 2013 5:24 PM in response to lanceloz

Sorry, I don't know the answer to that.

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Answer 7

Dec 16, 2013 5:47 PM in response to lanceloz

Yes. If you plug in wired Ethernet and it's higher in the service order, then it will take over and your transfer should speed up markedly. OS X has been able to do this since 10.3 at least 😉

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Answer 8

abwc2

Level 1

0 points

Dec 16, 2013 8:48 PM in response to lanceloz

What an outstanding thread.

Brilliantly-posed question; answer simple, efficient, and directly to the point; clarifying question and answer equally so.

AAA+ work, everyone.

Thank you !

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