MBP Connecting to Network with IPv6 Address

In system preferences > Network > Wi-Fi ...

set IPv6 to "link-local only"

This will maintain your Mac's ability to use IPv6 to discover network resources like Printers, but keep it from trying to use IPv6 to connect to the Internet or anything off-network.

Pick the ONE router closest to the Internet connection, and have that one (only) issue IP addresses via DHCP. Set the secondary Router as an access point (NO DHCP addreses issued) and it will defer to the main Router for device IP addresses.

If you give them the SAME Network-name and password, they will act as one network for your devices, and devices will automatically hand off to the the stronger one when one gets too weak.

That screen shows you have a connection. On 5GHz band, channel 48, using 802.11n protocol. You have attained a transmit rate of 240M bits/sec using two antennas. Your raw signal is -47 less noise at -90 yields signal to nose at 43, excellent.

What you DON"t seem to have is a connection to the Router that is issuing valid local DHCP addresses. I suspect there is a configuration error in the remote Router (or your special cable is unplugged).

The top-level information in the remote Router should be reporting the correct Address of the main Router, probably 192.168.1.1

Network Utility, in the Utilities folder, has a Ping function that you can use to check whether the remote Router can see the Main Router. You would enter 192.168.1.1 as the address to ping and the number of pings to send as 3, then say go. All packets lost says you are not connected.

"self-assigned IP address" vanishes the moment you can communicate with a Router that can give you a valid local IP address. In most cases, being "self-assigned IP address" indicates "no Router will talk to me".

This suggests either possible problems inside your MacBook Pro 2020, or marginal connection between your two Routers.

How are your two Routers connected ? {over-the-air, Ethernet cable, Powerline Ethernet}

If you place the MacBook very close to the remote Router, does it get an IP address then? If so, what does its Wi-Fi snapshot look like (invoked by holding Option and clicking on the Wi-Fi icon on the menuBar) ? it would be similar to this older one :

>> if you get a connection, please screenshot or transcribe that snapshot and post it back here.

One way to "tear it all out and start over" inside your Mac is to use a new, named Network Location File. Be sure to give it a new unique name so that its "starts over".

How to use network locations on your Mac - Apple Support

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There is one more thing to try on the Mac. Start up in Safe Mode.

"works in Safe Mode, fails in regular mode" implies "It's something you added."

<< other stuff connects to this router fine >>

how do you know that, for certain? Maybe other devices with better radios are connecting to the main Router.

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When you examine the parameters of remote Router, does it show that its gateway to the Internet is the Main Router?

can you ping back form a device on the main Router to the remote Router?

Thanks for reaching out mumbles2701.

It sounds like you're having trouble with your MacBook Pro connecting to the network. We can help get you on the right track.

According to Use IPv6 on Mac, this may be expected behavior for your MacBook Pro to connect using this protocol:

"IPv6 is a version of the Internet Protocol (IP) that provides more IP address space for internet users. This allows more addresses or nodes than are available under IPv4. IPv6 also provides more ways to set up the address and simpler autoconfiguration. By default, IPv6 is configured automatically, and the default settings are sufficient for the majority of computers that need to use IPv6."

If you are having trouble connecting to the internet with your second network, go ahead and check out the additional steps in If your Mac doesn't connect to the Internet over Wi-Fi.

See if that improves the situation, and keep us posted.

Take care!