[Samba] Domain accounts get throttled bandwidth

[Krzysztof Kucybała]

Hi all,
I have this really weird issue that I'm trying to figure out. I have a fair few computers and other network-attached devices at home. There are linux servers (1 physical debian buster hosting 2 virtual debian busters, one of which is my samba primary dc), linux desktops (3 kubuntu, 1 ubuntu) and a couple of windows 10 laptops. Aside of that some phones and a PS4 console. My ISP provides me with a static public IP address on a 400 D/40 U MBit lease line and it generally works. I set their router (some Hitron device) to bridge and I'm using Unifi Dream Machine Pro (previously used Unifi Security Gateway, the problem was visible there too) to run my local network but...

  1.  wifi devices such as phones seem to be getting whatever bandwidth their wifi chip allows, tops I've seen was 260MBit. PS4 is close to max as well. None of these devices have anything to do with my domain though...
  2.  windows laptops get max possible - if they're wired they max out the ISP connection on speedtest.net, on wifi it's slightly worse but still plenty above 100Mbit most of the time. This is regardless of who is logged on, and whether it's a local account or a domain account
  3.  linux desktops - this is the funny one. If I'm logged on with a local account, they max out the connection too, but as soon as I log on with a domain account, I get a bandwidth cap of 10Mbit download. Interestingly, upload doesn't seem to be capped, or it's capped above what I'm getting from the ISP, because speedtest.net routinely shows 40+ on the way up.

I would appreciate any hints as to where to even start troubleshooting this. I can't even say precisely when this problem surfaced for the first time, but it's certainly been a good few months.

One thing that comes to mind is to remove the Unifi router from the picture and see if that changes anything. I has a guest profile that can limit bandwidth, but I increased that limit to see if it was the culprit, and it had no effect. Removing it from the setup would be quite cumbersome, so I'd prefer to exhaust all simpler options (if there are any) before I take that road.


Below are my samba versions:
primarydc:

localadmin at primarydc:~$ dpkg -l | grep samba
ii  python-samba                   2:4.9.5+dfsg-5+deb10u1       amd64        Python bindings for Samba
ii  samba                          2:4.9.5+dfsg-5+deb10u1       amd64        SMB/CIFS file, print, and login server for Unix
ii  samba-common                   2:4.9.5+dfsg-5+deb10u1       all          common files used by both the Samba server and client
ii  samba-common-bin               2:4.9.5+dfsg-5+deb10u1       amd64        Samba common files used by both the server and the client
ii  samba-dsdb-modules:amd64       2:4.9.5+dfsg-5+deb10u1       amd64        Samba Directory Services Database
ii  samba-libs:amd64               2:4.9.5+dfsg-5+deb10u1       amd64        Samba core libraries
ii  samba-vfs-modules:amd64        2:4.9.5+dfsg-5+deb10u1       amd64        Samba Virtual FileSystem plugins

clients:
ii  python3-samba                              2:4.11.6+dfsg-0ubuntu1.9                      amd64        Python 3 bindings for Samba
ii  samba                                      2:4.11.6+dfsg-0ubuntu1.9                      amd64        SMB/CIFS file, print, and login server for Unix
ii  samba-common                               2:4.11.6+dfsg-0ubuntu1.9                      all          common files used by both the Samba server and client
ii  samba-common-bin                           2:4.11.6+dfsg-0ubuntu1.9                      amd64        Samba common files used by both the server and the client
ii  samba-dsdb-modules:amd64                   2:4.11.6+dfsg-0ubuntu1.9                      amd64        Samba Directory Services Database
ii  samba-libs:amd64                           2:4.11.6+dfsg-0ubuntu1.9                      amd64        Samba core libraries
ii  samba-vfs-modules:amd64                    2:4.11.6+dfsg-0ubuntu1.9                      amd64        Samba Virtual FileSystem plugins
ii  vlc-plugin-samba:amd64                     3.0.9.2-1                                     amd64        Samba plugin for VLC