Typical Problems on LTSP

Slow Network Speed

The terminal server is especially sensitive to slow networks. This is simply because the entire operating system is transferred over via the network. You should have at least a 100MB backbone for your network and you should be using switches not hubs. Remove the hubs as they will send messages to all computers on the network as they cannot isolate messages to an individual computer.

Ubuntu has several network cards that it is particularly problematic with. I have found that when I experience a slow connection the majority of the time it was a network card that had a bug in the Ubuntu implementation. Check to see if that is the case for your network card as replacing it with a different brand card often made a significant difference.

Another issue that may arise to slow down your network is the ipv6 implementation. Turn off ipv6 in Ubuntu and that may help as well.

SSH Key Regeneration

If you see this message you need to update the keys for your network card.

"This workstation isn't authorized to connect to server"

sudo ltsp-update-sshkeys
sudo ltsp-update-image

Be sure to do it in that order.

Firewall
You will want to do a lot of testing with the firewall before you call it good.  This is an area that often will cause you problems.  If you are using the ufw firewall then you will want to enable it first.

ufw enable

Linux Terminal Server Firewall (DHCP,SSH, Samba)
You will need to enable several ports for a LTSP server as it will provide DHCP on  ports 67,68 UDP and you may have Samba enabled on ports 139,445 and of course you will want SSH on port 22.

ufw allow 67/udp
ufw allow 68/udp
ufw allow 445/tcp
ufw allow 13/tcp