Migration Assistant ignored Thunderbolt connection

Question

I’m migrating from an MBP 2014 running Big Sur to an MBA M2 connected via Thunderbolt (via Apple’s T3-T2 adapter and Apple’s Thunderbolt cable), but Migration Assistant is using Wi-Fi.

How do I force MA to use the Thunderbolt connection?

• Allan: Did you set up networking for your Thunderbolt connections?
• orome: @Allan That’s not mentioned anywhere in the instructions. What does that entail? And can I stop and do that and restart?
• Allan: You don't need to restart. Just assign an IP addres (10.0.0.1 and 10.0.0.2 is fine) for each TB connection. If you must, just disable, then re-enable each interface. I forgot to ask... you're certain that you have a TB cable and not a USB-C cable, correct?
• orome: @Allan That’s the answer I think. (Cancelled, added a Thunderbolt networking interface on the source. Started again, deleting conflicting user on destination from aborted/skipped setup — and now it’s using Thunderbolt.)
• orome: @Allan Still pretty slow: 846 MB/s. Is that just my old (2014) source? Better than 5 MB/s over Wi-Fi!

Answer 1

How do I force MA to use the Thunderbolt connection?

For Migration Assistant to work over Thunderbolt, you need to implement IP over Thunderbolt. Apple has an excellent support document regarding this: Use IP over Thunderbolt to connect Mac computers

From Apple:

1. Connect a Thunderbolt cable to the Thunderbolt ports on the computers you want to connect.
2. On your Mac, choose Apple menu > System Settings, then click Network in the sidebar. (You may need to scroll down.)
3. Click the Thunderbolt Bridge service on the right, then click Details. If you don’t see a Thunderbolt Bridge service, you need to add one. See Set up a network service.
4. If you need to enter an IP address, click TCP/IP, click the Configure IPv4 pop-up menu, choose an option, then enter the IPv4 address in the IP address field. If needed, you can also enter a subnet mask and router address.
5. If you need to enter DNS or search domain addresses, click DNS, then enter the addresses.
6. Click OK

Essentially, you’re creating a simple point-to-point network (no router) by manually assigning IP addresses to each node at the ends of the Thunderbolt connection. Once this network is created, you can transfer data over it like any regular network.