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Direct Ethernet connection to Raspberry Pi/Odroid without router

The solution is based on running DHCP service at your workstation (your notebook for example), and use it to attribute an IP address to your Raspberry Pi/Odroid. Then use ssh to connect to your Raspberry Pi/Odroid through this IP address.

Terminology	Explaination
Client	Your Single Board Computer, such as a Raspberry Pi or an Odroid
Server	Your workstation with any linux based systems, like Ubuntu

Configuration at the Client Side (optional)

Enable SSH connection

for Raspberry Pi
```
sudo systemctl enable ssh
```
for Odroid
```
sudo vim /etc/ssh/sshd_config
```
find the line PermitRootLogin and set it to PermitRootLogin yes

Modify DHCP Client configuration
```
sudo vim /etc/dhcp/dhclient.conf
```
fin the line send host-name "foo"; and uncommented it

Configuration at the Server Side

Install a DHCP server
```
sudo apt-get install isc-dhcp-server
```
Use ifconfig to find your Ethernet network interface, it's probably eth0 but in my case it's enp61s0, then you need to configure a subnetwork on this interface

Backup your interface configuration file

sudo cp /etc/network/interfaces /etc/network/interfaces.original

Modify interface configuration file

sudo vim /etc/network/interfaces

which should be modified like the output below

auto lo
iface lo inet loopback

iface enp61s0 inet static
        address 192.168.1.1
        netmask 255.255.255.0
        network 192.168.1.0

Backup your configuration file of DHCP service

sudo cp /etc/dhcp/dhcpd.conf /etc/dhcp/dhcpd.conf.original

Modify the configuration file of DHCP service

sudo vim /etc/dhcp/dhcpd.conf

which should be modified like the output below

ddns-update-style	none;
default-lease-time 3600;
max-lease-time 7200;
authoritative;

subnet 192.168.1.0 netmask 255.255.255.0 {
  option routers 192.168.1.1;
  range 192.168.1.100 192.168.1.200;
}

Start the DHCP service by typing

# bring up the enp61s0 interface
sudo ifup enp61s0 
# start DHCP service
sudo service isc-dhcp-server start
# enable forwarding from the ethernet to wireless router
sudo /sbin/iptables --table nat -A POSTROUTING -o wlan0 -j MASQUERADE

Now plug your Raspberry Pi or or Odroid and open another terminal and tape
```
tail -f /var/log/sys/log
```
to test the connection, you should see an entry like

Dec 3 21:51:24 jzhou-Alienware-15-R3 dhcpd[10817]: DHCPACK on 192.168.1.100 to 00:1e:06:cb:e0:f5 (foo) via enp61s0
Then you can connect to your Raspberry Pi or or Odroid by
- for Odroid ssh [email protected]
- for Raspberry Pi ssh [email protected]

JinhaiZ/Direct_ethernet_connection.md

Direct Ethernet connection to Raspberry Pi/Odroid without router

Configuration at the Client Side (optional)

Configuration at the Server Side

Reference and Useful Resource