This Howto describes, how to interconnect wireless and wired network interfaces on the same Linux computer, to enable unmodified TCP/IP packets to pass from one interface to the other. In other places this is mentioned as network bridge or Wi-Fi line extender or Wi-Fi Internet share.

The reason for this HOWTO: the word bridge is misleading

For a network bridge we assume a device that transfers unmodified network packets from one network connection to the other. One can create a bridge device (virtual) and add members to it. This works only for bridge members of type wired - eth network cards. A network Bridge “connects” members on level 3 of the OSI model. That means communication on TCP/IP level.
When you want to add a Wi-Fi device to the bridge, you hit a barrier: Wi-Fi devices communicate on level 2 of the OSI model. You can find many manuals on the Internet that document how to circumvent this (in the form of putting the Wi-Fi card in 4addr mode). This simply DOES NOT WORK!
The Wi-Fi network card (member of the bridge) authenticates and connects to the Wireless Access Point (AP), but TCP/IP packets do not travel over the connection.
So searching for “wifi eth bridge” does not return any useful solution. The culprit is the word “bridge”.

A working solution is “Proxy ARP Routing”.
You simply enable IP forwarding and then for every device connected to the wired (eth) side of a “bridge” you have to add a routing line to the routing table. This can be automated by a program like parprouted - the Proxy ARP routing daemon.

Tested and working on Slackware64-14.2, kernel-4.11.6, CPU i5-7200

This solution is for static IP addresses. See below link of original source for a scenario that uses DHCP.

Assumptions:
We want to interconnect one Wi-Fi and one wired (eth) network card - the network devices wlan0 and eth0.
Prepare Slackware box so that you are able to communicate over the Wi-Fi adapter (using NetworkManager, rc.inet1 or other means…), making sure that the wired (eth) adapter is not being used.
I had set up WPA2 AES verification with NetworkManager to get a usable wpa_supplicant.conf configuration file which I used later with rc.inet1.
Disable all on-boot network configurations (i.e. make sure that rc.networkmanager or other files for network setup are not executable) and set rc.inet1 executable.

1. IP forwarding must be enabled in the kernel (since the 2.1 release the Linux kernel does not require an explicit compilation option for this)
2. download & compile & install http://www.hazard.maks.net/parprouted/parprouted-0.7.tar.gz
3. edit /etc/rc.d/rc.inet1.conf so to enable wlan0 and eth0. Assign them static IP addresses and set wlan0 to the lowest index and connect to the AP
   Below are example lines from /etc/rc.d/rc.inet1.conf - the only ones without comment sign “#” at the beginning and for WPA2 Wi-Fi authentication

   IFNAME[1]="eth0"
   IPADDR[1]="10.200.200.223"
   NETMASK[1]="255.255.255.0"
   
   GATEWAY="10.200.200.1"
   DEBUG_ETH_UP="no"
   
   IFNAME[0]="wlan0"
   IPADDR[0]="10.200.200.222"
   NETMASK[0]="255.255.255.0"
   USE_DHCP[0]=""
   DHCP_HOSTNAME[0]=""
   
   WLAN_MODE[0]=Managed
   WLAN_ESSID[0]="R7500"
   
   WLAN_WPA[0]="wpa_supplicant"
   WLAN_WPADRIVER[0]="wext"

4. set /etc/rc.d/rc.ip_forward executable:

   # chmod +x /etc/rc.d/rc.ip_forward

5. add a line

   /usr/local/sbin/parprouted wlan0 eth0

   to /etc/rc.d/rc.local and make sure that this file is executable

That's all. Reboot and you have a working Wi-Fi - eth bridge, also called Wi-Fi extender or Wi-Fi Internet share.

Note on parprouted compilation:
The parprouted man page section “Requirements” says: “parprouted requires the “ip” program from iproute2 tools to be installed in /sbin. If it is installed in another location, please replace ”/sbin/ip“ occurrences in the source with the correct path”.
Slackware installs the ip program as /sbin/ip so you should be OK.

Look below for a solution in a source link.

* Written by Zdenko Dolar, August 2017

* Original source:https://wiki.debian.org/BridgeNetworkConnectionsProxyArp