Set eth0 as DHCP in raspberry pi - linux

Question

I want to set eth0 of RPI (Raspbian Stretch) to be DHCP, my goal is that when I will connect any device that communicates using TCP/IP protocol, that device will receive an IP address.
I have found many guides that all lead to making eth0 ip address static, which is not my intention.
Currently a device is connected through eth0 , ifconfig says it has some IP but pinging the hostname of the device gets no reply. wlan0 is connected via wifi.
Here is some info :
pi#raspberrypi:~ $ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 169.254.31.197 netmask 255.255.0.0 broadcast 169.254.255.255
inet6 fe80::ad5a:8219:4c27:b59b prefixlen 64 scopeid 0x20<link>
ether b8:27:eb:f3:f2:87 txqueuelen 1000 (Ethernet)
RX packets 81 bytes 26568 (25.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 46 bytes 10544 (10.2 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 31 bytes 3472 (3.3 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 31 bytes 3472 (3.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.71 netmask 255.255.255.0 broadcast 192.168.0.255
inet6 fd01::60ff:8818:5965:dc58 prefixlen 64 scopeid 0x0<global>
inet6 fe80::473d:110e:5474:8000 prefixlen 64 scopeid 0x20<link>
ether b8:27:eb:a6:a7:d2 txqueuelen 1000 (Ethernet)
RX packets 955 bytes 74427 (72.6 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 184 bytes 22096 (21.5 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
pi#raspberrypi:~ $ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Please note that this file is written to be used with dhcpcd
# For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf'
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
Any advice to how to achieve my goal will be happily received.

Answer 1

Have you tried this: https://wiki.debian.org/NetworkConfiguration#Using_DHCP_to_automatically_configure_the_interface
i.e. just add this to /etc/network/interfaces:
auto eth0
allow-hotplug eth0
iface eth0 inet dhcp
if you're really pedantic you could create a file like /etc/network/interfaces.d/eth0-dhcp and paste these lines into it - the end result will be the same.

Answer 2

If you simply want to connect two devices (without routing/forwarding/etc), i.e. for a standalone test network, this should work:
Figure out what IP range you want to use, and what IP you want your
DHCP server to have (let's call it IP_DHCP)
Install isc-dhcp server
Set static IP address for eth0 (e.g. set it to the IP_DHCP you
chose earlier)
Configure /etc/dhcp/dhcpd.conf for the desired network range (man
dhcpd has a decent reference), make it authoritative (unless there
are other DHCP servers).
Run service isc-dhcpd-server start
Example of a configuration:
sudo apt-get install isc-dhcp-server
sudo nano /etc/conf/dhcpd.conf
Uncomment #authoritative to make it authoritative
Add along the following lines(customize based on what you decided in step 1), where routers is IP_DHCP:
subnet 10.0.0.0 netmask 255.255.255.0 {
range 10.0.0.1 10.0.0.100;
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;
option routers 10.0.0.1;
}
Save buffer and close
sudo service isc-dhcpd-server start
Good luck!
P.S. if you are getting connect:network not found issues, then you likely have an issue in your routing tables (route) setup.
Something along the lines of
sudo route add default gw 10.0.0.1
where the IP address is your eth0 will likely allow communication.

Answer 3

NetWork Manager (nmcli) might be running on the device and has been configured to work with a static IP.
The following commands can help you check if your device is managed by nmcli:
nmcli d
nmcli con show
Run the following command and replace 'Wired connection 1' with the name of your connection.
nmcli con show 'Wired connection 1' | grep 'ipv4.method'
ipv4.method will show "auto" if set to DHCP or "manual" if set to static.
http://www.intellamech.com/RaspberryPi-projects/rpi_nmcli.html