Connecting a new MacBook Air (2025) to ethernet cable but blocked by the Thunderbolt setting of the old MacBook Air (2015)

jackdawart wrote:

1. Mr Hoffman, could you please tell me why is it not a functional network? And what does that mean?

Remembering that I am sitting using an almost identical set up at this very moment.

With your new computer you don't have a functional network. You have the chicken & the egg problem.

All I am asking is if on the new computer when I plug the ethernet cable into the adapter and the new computer starts communicating and says

delete thunderbolt 2 or

2. disable thunderbolt 2

If I hit disable will I be able to re-enable the Thunderbolt 2 if I plug the ethernet cable back into the old computer.

If macOS itself is saying disable Thunderbolt 2 then that will only affect that particular Mac. All the modem should be seeing is the Ethernet connection & communication. Only your computer should be seeing the Thunderbolt part since macOS is tunneling the Ethernet protocols & communication through that USB-C adapter (or attempting to do so).

I am thinking, that so far, no one has encountered this situation and so my question remains unanswered.

That is because the majority of people are connecting to a router. Connecting directly to a modem will always be more troublesome until you have everything configured correctly.

Keep in mind that your modem is expecting to see your old laptop. It may not be able to grab an IP address as your modem/ISP may only work with your old laptop until you break that old connection....perhaps by power cycling the modem, or perhaps that is something the ISP will need to do. Also, once you get your new laptop working with a direct connection to the modem, you may not be able to connect the old laptop without going through all these difficulties again.....it all depends how your ISP & modem work. This is something only your ISP can answer.

If you go into System Settings > Network, you should see something like

If you then click on Thunderbolt Bridge, you should see something like

If you then click on Details…, you should see something like

I would suggest that if you are not using Thunderbolt Bridge (a.k.a. IP-over-Thunderbolt), and you see something other than "Inactive" on that third screen, that you go back to the second one and click on Make Inactive and see what happens.

Possibly you used Migration Assistant to transfer things from the old Mac to the new Mac and Migration Assistant copied the Thunderbolt Bridge configuration from the old Mac to the new one. Thus causing the conflict between the migrated Thunderbolt Bridget settings, and the settings for the USB-C to Ethernet adapter.

You could probably also delete the Thunderbolt Bridge service entirely, and then add a new one back at some later date if you ever wanted do networking over Thunderbolt. It appears that the System Settings > Network just lists groups of settings for network ports – and that "by default, Network settings already includes services for each of your network ports." I'm guessing that deleting a "network service" just deletes its settings, and tells the Mac not to use that network interface for now; and that it doesn't actually delete underlying hardware drivers.

Mac User Guide – Use IP over Thunderbolt to connect Mac computers – Apple Support

Mac User Guide – Set up a network service on Mac – Apple Support

This said, I would echo the others' caution about connecting your Mac directly to the Internet without a router.

I know on my old cable modem, if I wanted to connect directly to the cable modem instead of using a separate router, I had to reboot the modem with my computer connected to it via Ethernet.

Also, with many wireless routers you can completely turn off the wireless portion or at least not allow any wireless connections.....you can just use the router's Ethernet ports.

Edit: Make sure to have a default macOS network configuration selected prior to rebooting the modem. If you must have some special configuration for this modem connection to communicate properly, then make sure you configure it....may need to do this from a default config once you connect them together & reboot them.

HWTech wrote:

I know on my old cable modem, if I wanted to connect directly to the cable modem instead of using a separate router, I had to reboot the modem with my computer connected to it via Ethernet.

The details there depend greatly on the ISP, and on their gear.

An ISP of my acquaintance requires MAC spoofing, for instance. That was a “fun” escalation too, as the customer support techs denied MAC spoofing was needed, and the line techs directly acknowledged the requirement and then established the mapping. They effectively use it as a second password.

(Note to the reader: “MAC” here is Media Access Control, and not “Mac” the computer brand from Apple.)

Also, with many wireless routers you can completely turn off the wireless portion or at least not allow any wireless connections.....you can just use the router's Ethernet ports.

Yep. Or you buy your gear with separate functions in separate boxes.

jackdawart wrote:

Thanks, Bob, but I still don't see any reason for a router. We are running only one device from the modem... we are fine with that.

One big reason is so your computer is not exposed directly to the Internet which is what happens when you connect it directly to a modem. Routers have their own built-in firewall to block most outside connections to your home network.....or in your case to your single computer. I would never want my computer exposed directly to the Internet. 20 years ago we had a Windows PC hacked within minutes of installing a clean OS...think about that.....20 years ago. There are a lot more miscreants doing this today than back then. I've seen the attempts in my router's logs showing people on the Internet trying to access my home network, but are stopped by my router.

And, right at this very moment the computer I am working from is happily connected by an ethernet cable plugged into a Thunderbolt 2 bridge which is plugged into my computer.

I am simply trying to get my new computer to work in the same way.

My original question is above and as yet it has not been answered.

You may need to contact your ISP to have them assist you with that direct connection. Only they know exactly the steps needed & any custom settings required to get the new Mac connected. Like I said before, your modem may need to be power cycled so it can forget your old computer. Or they may be other steps required....perhaps something your ISP must do on their end. @MrHoffman mentioned some of the possibilities in his reply to my earlier post. ISP connections like this can be very difficult & complicated.

As for macOS, create a new Network Location. Configure the new Network Location like your older Mac. It may not be that simple depending on what your ISP requires.

Use network locations on Mac - Apple Support

From original post:

When I connect the ethernet cable to my new 2025 MacBook Air via the 'USB-C/Ethernet adapter plugged into the new MacBook,

the dialog box in System Preferences - Network tells me to 'delete' or 'disable' the Thunderbolt 2.

You are not using Thunderbolt 2 on your new Mac. What harm is there to delete or at least disable the Thunderbolt 2 interface? Your new Mac is using Thunderbolt4 now anyway.

Either your new USB-C to Ethernet Adapter is using the USB protocol, or it is using a Thunderbolt3 protocol. If you had not migrated from your old system or backup, then you would not have that Thunderbolt2 networking option configured at all and may not be having any problems establishing your connection. Maybe by configuring a new Network Location you can hold off deleting this Thunderbolt2 configuration, but I would at least disable it since it is obviously not working now & macOS suggested it (you can delete it later when you realize you no longer need it). Besides if it is brand new, then you can easily wipe it back to factory defaults & migrate again.

Edit: Changed the reference from @BobTheFisherman to @MrHoffman. I got mixed up on who replied to my other post regarding other difficulties with ISP connections.

jackdawart wrote:

Thank you kaz-c, HW Tech, Mr Hoffman, BobtheFisherman, and Servant of Cats.

Your input has been very valuable and I appreciate the time each of you has taken to consider my problem.

It helped me to be able to know and understand more of the technology so I could at least know what to ask.

You're welcome.

I ended up calling the ISP who sent a contract technician.

He actually had some problems with the installation but gracefully solved them.

Sounds like there may have been more going on with the ISP & connection.

I did go for a router, and of necessity, got saddled with WiFi which I did not particularly want.

Most of the problems are solved... there remains one small one.

Many routers allow you to turn off the WiFi portion so they are not broadcasting any SSID. Just make sure your laptop's is able to work using Ethernet first (turn off WiFi on laptop just to be certain you are testing the Ethernet).

Again, thanks for your generosity in sharing your time and knowledge.

Thanks for following up. We're glad you finally got it sorted out (or mostly sorted out since you did not want WiFi).

jackdawart wrote:

Thanks, kaz-k, for taking the time to answer.

I prefer to stay wired in with ethernet cable rather than run a router for Wi-Fi.

You connect the router to the modem then connect the router to your computer using an Ethernet cable. kaz-k did not suggest or say anything about WiFi.

jackdawart wrote:

There's something here I am not understanding.

We have a satelitte dish connected to a modem which connects to our computer by an ethernet cable.

When we were first set up, we had a choice of using a router connected to the modem to provide a WiFi signal

or to wire directly into the modem using an ethernet cable. We chose the ethernet cable.

Could you explain to me why we would need a router now?

The box you are calling a “modem” is likely providing what is commonly called a bridged configuration.

It is intended to allow direct connection to your own networking gear.

You would usually connect your own firewall box to the modem, a box which would provide firewall, routing, NAT, and probably also DHCP services, and quite possibly other services. Wired switches and Wi-Fi connections and computers can then all be added “behind” the firewall box.

This bridged configuration avoids having to deal with an ISP box providing firewall, NAT, DHCP, usually Wi-Fi, and other services. You own the whole network and all the gear, starting at the local LAN connection on the ISP modem.

You can likely also configure your own Mac for a direct wired connection into the modem, though how that works depends on your ISP requirements. In the most recent configuration I’ve set up for a site, the ISP required PPoE credentials and another related detail before the direct connection was allowed. In the install, this ISP PPoE account data was then connected to and configured into the firewall, and not into a Mac.

You’ll need ro know what network setup details are required for your ISP and for this modem.

Misconfigured networks can unstable, yes. How those networks might malfunction varies. And here, the details and requirements of the ISP modem — which usually expects to be connected to a customer-provided firewall / gateway / NAT box — matter.

As for your question, and since you undoubtedly have a complete and current backup here, try it. Whatever you do to Thunderbolt or other settings can be recovered with a wipe and restore.

I’d here consider asking the ISP for their firewall / gateway / NAT box too, or would expect to learn rather more about networking, and whatever networking gear you pick. The former path if you want some amount of ISP support. The latter if you want more familiarity with IP and IP gear.

Hi,

I think you need to connect router to your modem if your modem doesn't have router capability.

jackdawart wrote:

I did go for a router, and of necessity, got saddled with WiFi which I did not particularly want.

Most of the problems are solved... there remains one small one.

Most ISP-provided Wi-Fi boxes can be set to “bridged” or “transparent” mode, or can be removed entirely.

Again, thanks for your generosity in sharing your time and knowledge.

De nada.

jackdawart wrote:

There's something here I am not understanding.

We have a satelitte dish connected to a modem which connects to our computer by an ethernet cable.

When we were first set up, we had a choice of using a router connected to the modem to provide a WiFi signal

or to wire directly into the modem using an ethernet cable. We chose the ethernet cable.

Could you explain to me why we would need a router now?

You connect a router to the modem WAN port via Ethernet then you connect your local devices to the router using wifi or Ethernet LAN ports as preferred.