Network IP configuration

In Debian 9, "eth0" in the dual network port defaults to obtain IP
dynamically (that is, DHCP), and "eth1" is fixed to "192.168.150.1".

The configuration of "eth1" is done via the
"/etc/network/interfaces.d/eth1" file, which is the only modification
to the original Debian network configuration.

   linaro@bm1684:~$ cat /etc/network/interfaces.d/eth1
   auto eth1
   iface eth1 inet static
          address 192.168.150.1
          netmask 255.255.255.0
          dns-nameservers 192.168.150.1

If the user deletes this file, then "eth1" will become the same as
"eth0" to obtain the IP through DHCP; If the user wants to fix the IP
of "eth0", just create an "eth0" file in the
"/etc/network/interafces.d" folder, and it will take effect after
restarting.

Note that it is best not to configure the two network cards as the
same network segment, otherwise problems may occur.

Ubuntu System Configuration

In Ubuntu 20.04, the "eth0" interface is set to obtain an IP address
dynamically (DHCP), while "eth1" is configured with a fixed IP address
of "192.168.150.1".

The configuration for "eth1" can be found in the
"/etc/netplan/01-netcfg.yaml" file. You can modify this file to adjust
the network settings for your Ubuntu system.

   linaro@bm1684:~$ cat /etc/netplan/01-netcfg.yaml  | more
   network:
           version: 2
           renderer: networkd
           ethernets:
                   eth1:
                           dhcp4: no
                           addresses: [192.168.150.1/24]
                           optional: yes

If the user deletes this file, then eth1 will revert to acquiring an
IP address through DHCP, similar to eth0. If the user wants to assign
a fixed IP address to eth0 as well, they only need to add an eth0 node
(similar to eth1) in the /etc/netplan/01-netcfg.yaml file and then
restart for the changes to take effect.