Need a fresh perspective on laptop vs. hotspot...

[IDEngineer]

This has been driving me crazy for a couple of weeks now, so I need a "fresh set of eyes" please.

I have a OnePlus 8T cellphone on T-Mobile. Works great and I'm not looking to get into a slugfest over choice of hardware or carrier. I also have a Lenovo X260 laptop running Win7.

I used to be able to turn on the hotspot in the phone and then associate the laptop to the hotspot, giving me Internet access in the field. That stopped working a while back, for no obvious reason, and I haven't been able to fix it. Now I'm headed back into the field so I need to get this working again ASAP.

Details:

* Multiple other devices can successfully associate with the hotspot, including other cellphones, other laptops, etc. My own laptop is the ONE AND ONLY device that cannot use my cellphone's hotspot.

* My laptop can successfully associate with EVERY other access point everywhere - hotels, retail stores, coffee shops, hospitals, other phone hotspots. This includes the hotspot on my wife's identical OnePlus 8T cellphone which was purchased and configured on the same day at the same time at the same T-Mobile location. My own cellphone is the ONE AND ONLY access point my laptop cannot use.

* I have deleted and recreated the hotspot on the phone with different SSID's and passwords. No effect.

* I have deleted and recreated the wireless network profile on the laptop for my cellphone to track the above changes on my cellphone. No effect.

* I have tried enabling and disabling wireless "service" (things like IPv6, QoS Packet Scheduler, etc.). No effect. Even if I match those settings to another Win7 laptop that associates perfectly.

* I have confirmed that the security (WPA2-Personal) and encryption (AES) match on both devices.

To be clear: My laptop and cellphone both "see" each other and report that they are associated. My cellphone reports one device connected to its hotspot and reports its MAC address. Likewise, the laptop reports being associated with my cellphone's SSID. However, Internet packets will not transfer. Not even simple pings to something like 8.8.8.8. They associate, but they won't transfer data.

I need some suggestions of things to try. Thanks in advance!

[AndyBeez]

Might be some random but strict policy rule on the Win7 Defender / Firewall. Maybe a 'network' is getting blocked?? Look for the network and or firewall protection settings. After 2020 MS stopped supporting Win7 with security updates, so something might have got busted back then? Happy hunting.

[IDEngineer]

All firewalls, Defender, etc. disabled. Including all related Windows Services. Been true on every laptop I've owned from the day I received them. I don't need to be debugging Microsoft's code when I'm trying to debug my own.

No antivirus software installed. Bloatware that was present at purchase disabled, uninstalled, and associated Registry entries deleted. I run the barest OS environment possible.

I have two Win7 laptops running here on the bench right now. Both are associated with the cellphone. One (happens to be the older one) passes data, the other does not.

I'm baffled. I can't figure out if it's the laptop or the cellphone, since as noted above each works with EVERY other tested device. They just won't pass data between them.

[AndyBeez]

urm...

Adapter card (wifi) Ethernet properties hasve CP/IP and LLDP enabled?

IP on laptop is dynamic for the connection?

Phone does not have an alternate address reservation?

IP subnet conflicts?

[IDEngineer]

Adapter card (wifi) Ethernet properties hasve CP/IP and LLDP enabled?

I will check, but I don't remember seeing those configuration options in the Adapter Properies.

IP on laptop is dynamic for the connection?

Yep, both for local IP and DNS.

Phone does not have an alternate address reservation?

I humbly admit I don't know about that.

IP subnet conflicts?

Shouldn't be any since the hotspot uses DHCP, and I've forcefully disabled the Ethernet interface on the laptop to avoid interface contention/prioritization issues.

[pcprogrammer]

You wrote that it works with your wife's phone, which is the exact same model. Maybe a solution is to swap the sim cards and see if it still works, and then use the wife's phone as yours out in the field to at least have it working for now.

[james_s]

I can recall a couple of instances where two wireless devices simply would not talk to each other properly despite there being no obvious reason for them to be incompatible. I never did solve the problem in either case, only using a different network interface in the laptop got it working.

[Psi]

yes, i would swap sim cards and try it.

Also, try a usb wifi adaptor on your laptop so the MAC address is different (or you might be able to change the MAC it in the options of your current wifi adaptor).

I have heard of phone companies adding tethering blocks to users who do too much data when tethering.
Often when the phone plan is unlimited they are expecting users to do a typical "phone user" amount of data which is smaller than a full on desktop/laptop user.
So they make tethering against the rules if you read the fine print and can take action if they see you doing it too much.

[Whales]

They associate, but they won't transfer data.

This sounds like an IP or routing issue.

I recommend installing Wireshark on the laptop and monitoring all traffic on that interface.  On Linux you can monitor an interface even when it's not associated, that lets you set it up and then see the very first packets after connection is established (including DHCP), I presume it's similar on Windows.  See if anything weird happens, like ARP fights, and look inside the DHCP replies to see who has what IP address.

Also worth checking if windows has any weird routes set that might be hijacking things (eg all of 10.x.x.x/8).  I believe on windows the command is netstat -rn   It's possible that another network interface (VPN, tunnel, ethernet, etc) has some routes or IP ranges set that might interfere.

[pcprogrammer]

yes, i would swap sim cards and try it.

Also, try a usb wifi adaptor on your laptop so the MAC address is different (or you might be able to change the MAC it in the options of your current wifi adaptor).

I have heard of phone companies adding tethering blocks to users who do too much data when tethering.
Often when the phone plan is unlimited they are expecting users to do a typical "phone user" amount of data which is smaller than a full on desktop/laptop user.
So they make tethering against the rules if you read the fine print and can take action if they see you doing it too much.

If the problem moves to the other phone when swapping the sim cards the above might well be happening.

ISP's like to call this fair use policy, even if you have unlimited data 

[AndyBeez]

Another thought, is the phone's SSID top network priority?
Is the laptop automatically and silently connecting to another higher priority network in range?

[Psi]

Think back to when it was last working...

Did you happen to download 20GB ?

[IDEngineer]

Update: It appears that T-Mobile hotspotting requires IPv6 to route packets!

I noticed that IPv6 was disabled on the laptop in question. Only IPv4 was enabled. I enabled IPv6... and traffic started routing again. My guess is that if you don't obtain an IPv6 address from DHCP, your packets are simply ignored.

I have not been able to find any authoritative documentation for this, but it's definitely how things are behaving. I'm able to reproduce the behavior on other laptops now by enabling/disabling IPv6.

I will say that the responsiveness of the hotspot connection is dramatically lower than what I remember before the problem occurred. I don't know if T-Mobile dropped support for IPv4 addressing and their IPv6 address resolution is substantially slower, or if something else is going on. The throughput is the same once the sockets are connected, but the time to resolve DNS and establish TCP sessions is markedly slower. As a simple example, typing in "speedtest.net" requires 20-30 seconds to bring up the webpage, but then the throughput is the same as before. True for every website I've tried so far using IPv6.

[magic]

If it's DNS, manually configure a different DNS server like aforementioned 8.8.8.8.

If it's something else, then you have a problem.

[IDEngineer]

Continued testing reveals interesting results.

If I disable EITHER v4 or v6, no traffic is routed. Both protocols are required for anything to work.

I tried hard-configuring the DNS servers (while leaving DHCP to obtain the IP address) and the results are unreliable. Interestingly, I cannot ping 8.8.8.8 using that IPv4 address. I can ping it using its IPv6 address. So while both protocols are required, they are definitely not being treated equally!

There is a 10-30 second lag anytime a new site is visited. This does NOT occur with an Ethernet LAN connection on the machines used for testing so it's not a configuration problem with their browsers or overall TCP/IP stacks. It also doesn't occur when working through other WiFi access points (using IPv4). It's tempting to blame this on IPv6. However, it continues to be true that OTHER laptops do not slow down like this through my phone's hotspot.

So while we've sort of solved the problem by making sure both IPv4 and IPv6 are enabled, there's still a weird delay when new sites are accessed. It's almost like the local DNS cache demands a full domain download before proceeding... but only when on this hotspot. Once the site has been visited once, the entire site becomes very snappy.

[magic]

This ain't gonna far without Wireshark.

It's possible that their DNS server responds slowly, so try a different one. Over v4, v6, or carrier pigeons, whatever you want

It's possible, and perhaps much more likely, that the ISP's DNS responds quickly, but whenever you get both v4 and v6 addresses in the response, your system first tries v4 and then connects over v6 after v4 connection attempt times out. Try connecting to ipv6.google.com - this has no v4 address.

No idea why v4 suddenly stopped working. Could be something on your side. What are the IP addresses of the hotspot and the laptop, routes, etc?

[IDEngineer]

Here's some data. I'm typing this on the laptop while it's associated with the cellphone. Every switch of website takes 15-30 seconds and gives no indication that anything is happening, it just looks "stalled".

Here's the wireless interface's report from ipconfig /all:

Wireless LAN adapter Wireless Network Connection:

   Connection-specific DNS Suffix  . :
   Description . . . . . . . . . . . : Intel(R) Dual Band Wireless-AC 8260
   Physical Address. . . . . . . . . : F0-D5-BF-EB-96-AA
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   IPv6 Address. . . . . . . . . . . : 2607:fb90:c990:892b:d96e:e4b4:23f4:f853(Preferred)
   Temporary IPv6 Address. . . . . . : 2607:fb90:c990:892b:b5f3:3dbc:cad3:572a(Preferred)
   Link-local IPv6 Address . . . . . : fe80::d96e:e4b4:23f4:f853%15(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.254.175(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : Wednesday, December 14, 2022 6:02:20 PM
   Lease Expires . . . . . . . . . . : Wednesday, December 14, 2022 7:02:18 PM
   Default Gateway . . . . . . . . . : fe80::d8e2:74ff:fe4f:a6c5%15
                                       192.168.254.211
   DHCP Server . . . . . . . . . . . : 192.168.254.211
   DNS Servers . . . . . . . . . . . : 192.168.254.211
   NetBIOS over Tcpip. . . . . . . . : Enabled

Note it's getting DHCP addresses for both IPv4 and IPv6. I cannot disable either protocol or zero packets are routed. Note also the only DNS address is IPv4 despite IPv6 being configured to obtain a DNS address via DHCP, just like IPv4.

Here's a traceroute to ipv6.google.com:

C:\>tracert ipv6.google.com

Tracing route to ipv6.l.google.com [2607:f8b0:4009:81c::200e]
over a maximum of 30 hops:

  1     2 ms     2 ms     1 ms  2607:fb90:c990:892b::17
  2    79 ms     *       30 ms  fc00:10:6:122::254
  3    36 ms    25 ms     *     fc00:10:6:122::254
  4     *        *        *     Request timed out.
  5     *        *        *     Request timed out.
  6     *        *        *     Request timed out.
  7     *        *        *     Request timed out.
  8    95 ms    49 ms    50 ms  2001:4860:0:1::6300
  9    50 ms    44 ms    54 ms  2001:4860:0:1006::f
 10    60 ms    54 ms    44 ms  2001:4860::c:4001:e418
 11    75 ms    68 ms    55 ms  2001:4860::c:4001:fb3f
 12    87 ms    85 ms    82 ms  2001:4860::c:4002:6b07
 13    85 ms    79 ms    80 ms  2001:4860::c:4000:d2a0
 14     *        *        *     Request timed out.
 15   139 ms    85 ms    81 ms  2001:4860:0:1::5687
 16    89 ms    85 ms    78 ms  ord38s33-in-x0e.1e100.net [2607:f8b0:4009:81c::200e]

Trace complete.

It appears we reach Google by the 8th hop, then bounce around inside their network until finally reaching the target IP at hop 16. Latency isn't too bad.

[magic]

These return times don't look too bad. I suppose that if you type ipv6.google.com into a browser it loads faster than google.com.

Can you trace a v4 only site like eevblog.com?

It looks like both protocols are enabled indeed, and you have addresses and default routes configured for each (the hotspot, presumably/hopefully).

[Infraviolet]

To be fully sure if there is an issue within your laptop's OS, or whether it lies elsewhere, have you tried live booting the laptop from a USB and seeinf if the fresh OS can connect to the wifi hotpsot using the laptop's hardware? If not your problem isclearly in the laptop's hardware rather than it's OS. And you've said every device you've tried except that specific laptop connects just fine?