Hello
I have got Raspberry pi Model 3:
INTERNET ====> eth0 (RP3) (192.168.1.50) perfect.
(RP3)===> WiFi HotSpot (Dietpi) (192.168.42.1) perfect witch DHCP WIFI.
(RP3)===> eth1 (USB ETHERNET LAN) ??? (DHCP?).
it’s possible with usb ethernet (eth1) have got DHCP SECOND + SWITCH ==> Second lan witch DHCP? 
Sorry my bad English.
Sorry my bad English.
Nothing to be sorry about. Nobody is perfect, including us We are all human 
Back to your questions. Just to avoid a misunderstanding and for clarification on your setup
eth0 is acting as DHCP client and is receiving an IP address
wlan0 (HotSpot) is acting as DHCP server and is providing IP address to client connected to the HotSpot
eth1 (USB) needs to be configured manually (not possible via dietpi-config). What exactly is the use case for this adapter? Where is it connected to? Same network as eth0? A different network? With a different DHCP server? Some more information on your scenario would be helpful.
Thanks
Yes, eth1 is USB-ETHERNET.
Eth1 is connect an switch TP-LINK SG108E.
I would like eth1 to have a different dhcp server than HotSpotwifi.
Router → RPi (eth0) → RPi (wlan0 and eth1) → Two subnet for my devices (First wlan0 (ok) and Second eth1 (?).
Does the RPi should act as DHCP server for eth1? Do you already configured eth1?
Sure, dietpi for the two DHCP servers. I don’t know how to configure eth1 to have its own DHCP server. One server works fine (HotspotWifi), the other doesn’t (eth1) 
.
As already told above, we don’t configure or manage an interface eth1. It’s simply not taken into account by our script’s. Therefore you would need to configure it manually. First your would need to get your USB Ethernet interface up and running using a STATIC IP for this interface. Means, you would need to define the IP range/subnet you like to use 192.168.x.1. I guess this you have not done yet?
ip a
Once you have the basic interface configured, you could adjust DHCP server configuration to serve both interfaces.
The only thing I have done was:
nano /etc/network/interfaces
eth1
static 192.168.12.1
I don’t know how to create a second DHCP server with 192.168.12.X
I don’t know what I have to configure.
You can have a second dhcp server on eth1. I think the easiest way is to add another pool in the existing dhcp server for eth1.
For configuring eth1, you’ll need some more things:
allow-hotplug eth1
iface eth1 inet static
address 192.168.12.1
netmask 255.255.255.0
If you edit the /etc/network/interfaces directly, keep in mind that using dietpi-config will overwrite them. You can use drop-ins in /etc/network/interfaces.d/ which won’t be affected.
As already stated, ensure your eth1 is correctly configured. You could use ip a to check all interfaces available
For the hotspot we use isc-dhcp-server. Therefore you would need to add the new network segment to /etc/dhcp/dhcpd.conf to allow DHCP on it.
Thanks to Joulinar and trendy.
It doesn’t work with the information you gave me .
nano /etc/network/interfaces
# Ethernet 2
allow-hotplug eth1
iface eth1 inet static
address 192.168.12.1
netmask 255.255.255.0
nano /etc/dhcp/dhcpd.conf
# Hotspot (OK, DHCP+PIHOLE)
subnet 192.168.42.0 netmask 255.255.255.0 {
range 192.168.42.10 192.168.42.50;
option broadcast-address 192.168.42.255;
option routers 192.168.42.1;
option domain-name "local";
option domain-name-servers 192.168.42.1;
}
# ETH1 (Dont Work , NO DHCP + PIHOLE)
subnet 192.168.12.0 netmask 255.255.255.0 {
range 192.168.12.10 192.168.12.50;
option broadcast-address 192.168.12.255;
option routers 192.168.12.1;
option domain-name "local2";
option domain-name-servers 192.168.12.1;
}
After making the changes,reset raspberry pi , it still doesn’t work
Should we do more?..
I don’t have DHCP on eth1 + TL-SG105E.
the question still not answered, is your USB-Ethernet interface working? Did you checked it using ip a? Are you able to ping yourself on the USB-Ethernet interface?
To verify the DHCP server working, you could use nmap
apt install nmap
nmap --script broadcast-dhcp-discover -e <interface_name>
As well you might need to setup some iptables rules to be able to forward traffic from USB-Ethernet interface to eth0.
Thank you,i will try it Joulinar
Also check the DHCP server logs to see whether it is correctly consider the additional interface:
journalctl -u isc-dhcp-server
If clients shall have Internet access through the Pi, then also additional IP forwarding rules are required. Check the /etc/iptables.ipv4.conf (or something like that) file about how this is done for wlan0/eth0, and how it is invoked in /etc/network/interfaces. Generally I recommend to move the eth1 settings into an own config file in /etc/network/interfaces.d, so they don’t get accidentally overwritten by dietpi-config or dietpi-software when reinstalling or reconfiguring the WiFi hotspot.