Original link: Devices without network card use Raspberry Pi wifi to network | DHCP | No Debug (fater.top)
Use a wired network card and a wireless network card of the Raspberry Pi to convert wifi into a wired signal, so that devices without a network card can directly connect to the Raspberry Pi for Internet access
cause
There is a beggar’s version of the NUC motherboard at hand, no wifi, no bluetooth, only two wired network ports, but the room is too far away from the main router, and it is very inconvenient to pull the network cable to connect. In line with the principle of using what you can, I happened to bring the Raspberry Pi with me when I went home this time, so I squeezed the two network cards of the Raspberry Pi to let this NUC motherboard go online. In addition, the Raspberry Pi and NUC motherboards are both without screens. When necessary, I use a video capture card to display on the screen of my laptop. Most operations can be completed through ssh.
Equipment/environment introduction
Main router: radio and television network, basically no room for operation
Bypass router (hereinafter referred to as Raspberry Pi): Raspberry Pi 4B 4G, arrch, Ubuntu20.04, a wired network port (eth0), a wireless network card (wlan0)
Devices that need to be connected to the Internet (hereinafter referred to as nuc): industrial control motherboard, amd, Ubuntu20.04, dual limited network ports, no wireless network card
PC: Notebook, Windows 11, no network port
Main routing gateway: 192.168.1.1
Bypass router ip: 192.168.1.24
Plan configuration service: DHCP range 172.21.252.2-172.21.252.254; gateway address is 172.21.252.1
Schematic diagram:
configuration process
Preparation
Make sure the Raspberry Pi is connected to wifi, use PC to connect to SSH
ssh ubuntu@192.168.1.24
Configure Raspberry Pi eth0 interface
Open eth0 and specify ip as 172.21.252.1
ifconfig eth0 172.21.252.1 netmask 255.255.255.0 up
Configure DHCP service
Use dnsmasq to provide DHCP service for eth0 network card
install dnsmasq
sudo apt install dnsmasq
Add /etc/dnsmasq.conf configuration
sudo nano /etc/dnsmasq.conf
port=0 interface=eth0 listen-address=172.21.252.1 dhcp-range=172.21.252.2,172.21.252.254,12h
Explain the configuration parameters
interface=eth0 is to set the dhcp service interface as the wired network card on the Raspberry Pi
listen-address=172.21.252.1 is to set the listening address to the ip address of the limited network card
dhcp-range=172.21.252.2,172.21.252.254,12h is to set the ip range assigned by DHCP, from 172.21.252.2 to 172.21.252.254, and the lease time limit is 12h
Note that if you do not set `
port=0` will open the dns service, but we don’t need it. Set it to 0 to indicate that the dns service is closed. If it is not set, the following error may appear, which means that port 53 has been occupied. The solution can be to close the dns service or set the Set it to another port, such as 5533
Jan 16 02:49:30 ubuntu systemd[1]: Starting dnsmasq - A lightweight DHCP and caching DNS server... Jan 16 02:49:30 ubuntu dnsmasq[1570]: dnsmasq: syntax check OK. Jan 16 02:49:31 ubuntu dnsmasq[1571]: dnsmasq: failed to create listening socket for port 53: Address already in use Jan 16 02:49:31 ubuntu dnsmasq[1571]: failed to create listening socket for port 53: Address already in use Jan 16 02:49:31 ubuntu dnsmasq[1571]: FAILED to start up Jan 16 02:49:31 ubuntu systemd[1]: dnsmasq.service: Control process exited, code=exited, status=2/INVALIDARGUMENT Jan 16 02:49:31 ubuntu systemd[1]: dnsmasq.service: Failed with result 'exit-code'. Jan 16 02:49:31 ubuntu systemd[1]: Failed to start dnsmasq - A lightweight DHCP and caching DNS server.
Restart the dnsmasq service
sudo systemctl restart dnsmasq
After running correctly, execute sudo systemctl status dnsmasq output should be roughly as follows:
● dnsmasq.service - dnsmasq - A lightweight DHCP and caching DNS server
Loaded: loaded (/lib/systemd/system/dnsmasq.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2023-01-16 02:51:26 UTC; 1min 0s ago
Process: 1606 ExecStartPre=/usr/sbin/dnsmasq --test (code=exited, status=0/SUCCESS)
Process: 1607 ExecStart=/etc/init.d/dnsmasq systemd-exec (code=exited, status=0/SUCCESS)
Process: 1616 ExecStartPost=/etc/init.d/dnsmasq systemd-start-resolvconf (code=exited, status=0/SUCCESS)
Main PID: 1615 (dnsmasq)
Tasks: 1 (limit: 4433)
CGroup: /system.slice/dnsmasq.service
└─1615 /usr/sbin/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dp>
Jan 16 02:51:25 ubuntu systemd[1]: Starting dnsmasq - A lightweight DHCP and caching DNS server...
Jan 16 02:51:25 ubuntu dnsmasq[1606]: dnsmasq: syntax check OK.
Jan 16 02:51:26 ubuntu dnsmasq[1615]: started, version 2.80 DNS disabled
Jan 16 02:51:26 ubuntu dnsmasq[1615]: compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua TFTP connt>
Jan 16 02:51:26 ubuntu dnsmasq-dhcp[1615]: DHCP, IP range 172.21.252.2 -- 172.21.252.254, lease time 12h
Jan 16 02:51:26 ubuntu systemd[1]: Started dnsmasq - A lightweight DHCP and caching DNS server.
lines 1-17/17 (END)Enable SNAT
The ip_forward of Ubuntu 20.04 is disabled by default and needs to be enabled manually. Edit the /etc/sysctl.conf file to find the line net.ipv4.ip_forward=1 and uncomment it
sudo nano /etc/sysctl.conf
Configure snat to connect to the external network
iptables -t nat -A POSTROUTING -s 172.21.252.1/24 -o wlan0 -j MASQUERADE
Among them, 172.21.252.1/24 is the network segment of DHCP, and wlan0 is the wireless network card of Raspberry Pi
Set up nuc networking
Connect the raspberry pie to the nuc with a network cable, monitor the connection on the raspberry pie to get the ip of the nuc
ssh connection nuc
ssh ubuntu@172.21.252.137
At this time, the nuc still has no way to access the external network through the domain name, and the DNS server address of the nuc needs to be set.
sudo nano /etc/resolv.conf
write nameserver 192.168.1.1 to file, save and exit now ping baidu.com can pass
Device network information
raspberry pie
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.21.252.1 netmask 255.255.255.0 broadcast 172.21.252.255
inet6 fe80::dea6:32ff:fe46:33fa prefixlen 64 scopeid 0x20<link>
ether dc:a6:32:46:33:fa txqueuelen 1000 (Ethernet)
RX packets 383 bytes 65536 (65.5 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 524 bytes 57530 (57.5 KB)
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 212 bytes 17610 (17.6 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 212 bytes 17610 (17.6 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.24 netmask 255.255.255.0 broadcast 192.168.1.255
ether dc:a6:32:46:33:fb txqueuelen 1000 (Ethernet)
RX packets 3670 bytes 583206 (583.2 KB)
RX errors 0 dropped 2 overruns 0 frame 0
TX packets 3837 bytes 796006 (796.0 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0nuc
enp2s0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
ether 00:90:27:e9:01:b9 txqueuelen 1000 (ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0x50800000-508fffff
enp3s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 172.21.252.137 netmask 255.255.255.0 broadcast 172.21.252.255
inet6 fe80::108b:c57d:1fab:fe4a prefixlen 64 scopeid 0x20<link>
ether 00:90:27:e9:01:ba txqueuelen 1000 (ethernet)
RX packets 472 bytes 52274 (52.2 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 399 bytes 65238 (65.2 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device memory 0x50500000-505fffff
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 1998 bytes 145444 (145.4 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1998 bytes 145444 (145.4 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0