Problem tethering Android 7.1.1 phone Posting this for the benefit of others, after failing to find the problem/resolution on my own.

Yesterday (Oct 2018), my Samsung J5 2016 phone failed to properly enable internet-wireless tethering. It never had a problem in the past, and I am fairly certain that I used tethering since date of the latest OS update (Jun 2018), at least in conjunction with an iOS device (iPad). But as of yesterday, tethering my Microsoft Surface Pro stopped working. 

What actually failed:


DNS resolution


Things I tried:


I restarted the Android device
I restarted the client (Surface Pro/Win 10)
I renewed the DHCP lease. (ipconfig /renew)


What worked:


Pinging the device. 
Pinging hosts by IP on the internet.
Manually configuring the interface to use a DNS server (8.8.8.8)
Manually configuring the interface to use the device as a DNS server (192.168.43.1)


What I did to resolve the issue:

First, on Windows, I used ipconfig /all to determine the DHCP assigned IP address and DNS addresses. I noted these two were different:


IP Address: 192.168.43.161
IP Address of Gateway: 192.168.43.1
DNS Address: 192.168.0.1


The DNS address looked bogus to me. 

On the Windows device, I used Zenmap (nmap) to discover available ports, and saw that for 192.168.0.1, ports 80 and 443 were available, but not 53. I then did a scan of 192.168.43.1 and saw that 53 (UDP and TCP) were available.
After trying some solutions (such as adding "dun" to the APN Type), I finally did a reset of all networking settings and rebooted the device. The next time I started tethering, I noticed that it also reset the SSID and password of the tethering setup. I then recreated the SSID, but forgetting the password, I entered a new password. On Windows 10, I could not seemingly change the password, and was therefore forced to "Forget the Wireless Network" and re-connect to it. 

One of these two steps solved the problem. I recommend first doing a "forget" on the Windows client, and if that doesn't work, "Reset Network Settings" on the device.