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So, I'm doing a 100+GB transfer over my LAN from my iMac to my NAS, I was simply wondering if it would utilize both the ethernet and the wifi for the transfer. If not, is there a way to enable transfers to use both?

  • I've edited out the second part of your question. Questions work better if they focus on one topic, also the second part is highly depending on your setup and there probably isn't a specific answer for that. – nohillside Jan 16 at 8:57
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    That would be a very bad idea. There are multiple questions and answer about this on Network Engineering and Server Fault about using multiple interfaces for a single traffic flow. That can cause a slower transfer. See this answer among many. – Ron Maupin Jan 17 at 0:57
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Do LAN transfers use both Ethernet and WiFi by default?

No. The default action is to use the one with the highest priority. This is usually done by the order of the interfaces that you specify in Network Preferences. Following that, the next order of priority is network latency.

If not, is there a way to enable transfers to use both?

What you are referring to is called link aggregation or bonding. Your Mac is definitely capable of doing this, however, you must connect to a switch (usually a "smart switch") that also has this capability. So, unless your switch has this ability, you can't do it.

Also, you can't bond WiFi and Ethernet; link aggregation is for bonding Ethernet links.

  • Is it possible to use an AP in order to have both links as ethernet? Or link aggregation doesn't work like regular packets? – Filipe Nicoli Jan 16 at 17:17
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    Link aggregation won't work over a single TCP connection either which is what the SMB file transfer is. Link aggregation takes special care to ensure all packets on a single connection go on the same link. You have to utilize special multi-stream protocols to make it work in this case. – user71659 Jan 16 at 19:23
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    @user71659 It can work for a single TCP connection if both endpoints support MPTCP. But MPTCP is not widely supported. – kasperd Jan 16 at 22:08
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If not, is there a way to enable transfers to use both?

Yes. While it is complicated (or, with cheaper devices, impossible) to do this on the link, network, or routing layers, you can use both Ethernet and Wifi by "bundling" your two links on the application layer easily.

Put both your devices on Ethernet and Wifi; and make sure Ethernet/Wifi are in different subnets. Then split your 100GB of files into two sets, their size roughly corresponding to the relative speed of the two connections.

Then, connect from the iMac to the NAS twice at the same time, once for each of the two IP addresses of the NAS. I have used a Mac one time in my life, about 20 years ago, so I have no idea how you do that, but I am still sure that it is somehow possible (in the worst case, by not mounting the NAS file system directly on the iMac, but by using something like a scp/ftp/rsync file transfer instead.

Then transfer the two sets of files you separated earlier, one to the first IP address, the other to the other. The TCP/IP traffic will go over the respective link only, and assuming that both devices are able to handle that capacity (i.e., the drives are fast enough, no artificial bottleneck due to badly optimized network stacks, etc.), you will get a maximum performance close to the sum of the two bandwiths.

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No, first priority is the wired lan. If lan is disconnected then wifi is used.

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    Do you have any source for that? Why should a wired connection have a higher priority? – Nico Haase Jan 17 at 13:24
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    Depends on the routing table, and the interface metric. Wireless interfaces typically have a higher metric (=> higher cost, less likely to be chosen) – Caius Jard Jan 17 at 16:30
  • I have used both ethernet and wireless network on my laptop connected to same network. The windows uses only lan network. In case lan is not working or connected to internet then wireless is used even though lan is connected. – Arvind Bakshi Jan 17 at 17:25
  • At least on Linux, interface priority is configurable, but yes, ethernet has higher priority. However, it doesn't mean you'll always use that interface, since you might as well be connected to two different subnets. – Filipe Nicoli Jan 17 at 17:43

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