Mint 21.1 - IPv4 shows as "unknown" = some sites load, others don't

[ghost123uk]

Hi all.

I recently upgraded 3 laptops and a PC from Mint 20 to Mint 21.1.
I replaced the spinning metal drives with SSD ones. All seemed OK.

However, since then, all of them work fine on the main router, but when I try to connect to my Netgear Wi-Fi extender all the entries in "Connection information" show the word "unknown" in the IPv4 section. Some websites will load, but others (including this one, and the BBC for example) will not load at all. I get = This site can’t be reached Check if there is a typo in www."website name here"
DNS_PROBE_FINISHED_NXDOMAIN

If I put the old hard drive(s) back in (Mint 20), all is fine.
My Smart TV, my phone and my Firestick all connect to this extender and all websites load just fine.
I have checked the settings (on all 4 computers) in Network Connections and all seems correct (IPv4 set to Automatic as usual).

I have done a full factory re-set on this extender, and re-made the connection to my router = no change.

Does anyone have any thoughts on this please?

Thanks in advance,
John in the middle of the UK

[ghost123uk]

Ummm, obviously a tricky one this is.............

[Coggy]

That sounds very odd. At this point, I would not trust the GUI. Use the terminal to see what's really happening.
Compare the results between the 2 wifi points.
Firstly, look at the IP addresses with the command ip addr.
Secondly, look at the routing table ip route.
But I think the most likely issue is something related to DNS. Try host -v forums.linuxmint.com in both locations.

Do they start working if you leave them on the extender for 30 minutes? I'm wondering if it might be an ARP cache problem related to a change in MAC address when you switch access points.

Ultimately, I would want to use tcpdump to see what's really happening on the wire, but the above tests may give us a clue what to look for.

[rene]

There have been Wi-Fi connection issues with the 5.15 kernel. As far as I can quickly find this should be fixed also in the Ubuntu/Mint 5.15 series meaning that if the systems are up to date you should be good -- but if you are on 5.15 I'd still try a newer series kernel via Update Manager -> View -> Linux Kernels, even if only to rule it out.

[t42]

Depending on model it is possible to integrate Netgear Wi-Fi extender in the network in so many ways. Even for wild guess original description is too ambiguous.