Raspberry Pi Wifi Router/Repeater Howto

Definition

The Broadcom bcm2835, onboard Raspberry Pi 3, can be configured as an access point, wifi client, and router, comprising a wifi router or repeater.

Objective

To apply this procedure to configure a Raspberry Pi 3 as a wifi router or repeaer.

Elements (chrononological) (uc)

1. Verify hardware support
   • A wifi router or relay needs an AP cabable device.
   • A wifi relay needs a combined or additional managed device.
   • Examine wifi capable hardware.

     	      iw list
     	      # ...
     	      # Supported interface modes
     	      #   IBSS
     	      #   managed
                   #   AP
     	      #   monitor
                   #   P2P-client
                   #   P2P-GO
                   #   P2P-device
     	      # ...
     	      # Frequencies   ... 24xx MHz ... 5xxx MHz
     	      #
     	      # interface combinations are not supported
                   # valid interface combinations:
                   #   * #{ managed } <= 1, #{ P2P-device } <= 1, #{ P2P-client, P2P-GO } <= 1,
                   #     total <= 3, #channels <= 2
                   #   * #{ managed } <= 1, #{ AP } <= 1, #{ P2P-client } <= 1, #{ P2P-device } <= 1,
                   #     total <= 4, #channels <= 1
     	      # ...
     	  

     • Interface modes

       IBSS

       ad-hoc

       for host in CDMA LAN without access point or router

       managed

       for client host in LAN with access point

       AP

       for acces point in LAN with managed hosts

       P2P-*

       Wi-Fi Direct

       for hosts paired similar to Bluetooth

     • If AP and managed interface combinations are supported, one device might be used simultaneously as relay client and access point. (The Raspberry Pi Zero W and Raspberry Pi 3 AP/managed interface combination is restricted to 1 channel, and therefore unsuitable as single-device relay unless the LAN a single fixed channel.)
2. Install hostapd, dnsmasq, and udhcpd
   • If necessary add raspbian repository to /etc/hosts

     	  cat <<EOF | sudo tee -a /etc/hosts
     
     	  # Raspbian repository
     	  93.93.128.193      mirrordirector.raspbian.org
     	  208.69.120.55      mirror.nexcess.net
     	  EOF
     	  

   • If necessary configure access to internet

     	      sudo /sbin/route add default gw 192.168.1.254
     	  

   • Install hostapd, dnsmasq, and udhcpd.

     	  sudo apt-get install hostapd dnsmasq udhcpd
     	  

3. For safety, it is wise to move-copy-edit-diff complicated files, lest you accidently render your image unbootable. If you make a mistake simply move the .orig file back in place and try again.
4. Configure access point.

   	  cat <<EOF | sudo tee /etc/hostapd/hostapd.conf
   	  interface=wlan0
   	  driver=nl80211
   	  ssid=WIFINAME
   	  hw_mode=g
   	  channel=6             # 1, 6, or 12
   	  macaddr_acl=0
   	  auth_algs=1
   	  ignore_broadcast_ssid=0
   	  wpa=2
   	  wpa_passphrase=PASSWORD
   	  wpa_key_mgmt=WPA-PSK
   	  #wpa_pairwise=TKIP	# You better do not use this weak encryption (only used by old client devices)
   	  rsn_pairwise=CCMP
   
   	  # The following are peculiar to Raspberry Pi
   	  ieee80211n=1          # 802.11n support
   	  wmm_enabled=1         # QoS support
   	  ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]
   	  EOF
         

5. Configure dns server.

   	  cat <<EOF | sudo tee /etc/dnsmasq.conf
   	  interface=wlan0
   	  driver=nl80211
   	  ssid=WIFINAME
   	  hw_mode=g
   	  channel=6             # 1, 6, or 12
   	  macaddr_acl=0
   	  auth_algs=1
   	  ignore_broadcast_ssid=0
   	  wpa=2
   	  wpa_passphrase=PASSWORD
   	  wpa_key_mgmt=WPA-PSK
   	  #wpa_pairwise=TKIP	# You better do not use this weak encryption (only used by old client devices)
   	  rsn_pairwise=CCMP
   
   	  # The following are peculiar to Raspberry Pi
   	  ieee80211n=1          # 802.11n support
   	  wmm_enabled=1         # QoS support
   	  ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]
   	  EOF
         

6. Add LAN hosts otherwise misreported by /etc/hosts

   	  cat <<EOF | sudo tee /etc/hosts.dnsmasq
   	  ...
   	  192.168.7.1         raspberrypi-or-myhostnam raspberrypi-or-myhostnam.mydomain
   	  ...
   	  EOF
         

7. Configure dhcpd.

   	  sudo mv /etc/udhcpcd.conf{,.orig}
   	  sudo cp /etc/udhcpcd.conf{.orig,}
   	  sudo vi /etc/udhcpd.conf
   	  diff /etc/udhcpcd.conf{.orig,}
   	  ...
   	    # The start and end of the IP lease block
   	  - start           192.168.0.20    #default: 192.168.0.20
   	  - end             192.168.0.254   #default: 192.168.0.254
   	  + start           192.168.3.192   #default: 192.168.0.20
   	  + end             192.168.3.253   #default: 192.168.0.254
   	  ...
   	    # The interface that udhcpd will use
   	  - interface       eth0            #default: eth0
   	  + interface       wlan0           #default: eth0
   	  ...
   	  - opt     dns     192.168.10.2 192.168.10.10
   	    option  subnet  255.255.255.0
   	  - opt     router  192.168.10.2
   	  - opt     wins    192.168.10.10
   	  - option  dns     129.219.13.81   # appened to above DNS servers for a total of 3
   	  - option  domain  local
   	  + opt     dns     192.168.3.1
   	  + opt     router  192.168.3.1
   	  + option  domain  localnet
   	  ...
   
   	  sudo mv /etc/default/udhcpd{,.orig}
   	  sudo cp /etc/default/udhcpd{.orig,}
   	  sudo vi /etc/default/udhcpd
   	  diff /etc/default/udhcpd{.orig,}
   	    ...
   	    # Comment the following line to enable
   	  - DHCPD_ENABLED="no"
   	  + # DHCPD_ENABLED="no"
   	    ...
         

8. configure wifi interface
   • Set access point interface at boot

           cat <<EOF | sudo tee /etc/network/interfaces.d/012_wlan0ap
     	    # Enable wifi at boot
     	    auto wlan0
     
     	    iface wlan0 inet static
     	        address 192.168.3.1
     	        netmask 255.255.255.0
     	        network 192.168.3.0
     	        broadcast 192.168.3.255
     	    EOF
     	  

   • Set wifi client interface at boot

           cat <<EOF | sudo tee /etc/network/interfaces.d/013_wlan1
     	    # Enable wifi at boot
     	    auto wlan1
     	    iface wlan1 inet static
     	        wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
     	        address 192.168.4.68
     	        netmask 255.255.255.0
     	    EOF
     	  

   • Remove conflicting /etc/network/interfaces.d/*

     	  sudo mkdir -p /etc/network/disabled_interfaces.d
     	  sudo mv /etc/network/{,disabled_}interfaces.d/nnn_obsolete
     	  

     /
9. If desired, remove internet access

   	  sudo /sbin/route del default gw 192.168.1.254
         

Equipment

• running Raspberry Pi 3
• live access to Raspbian repository
• linux laptop for programming
  • ssh(1)
  • rsync(1)
  • wifi client capability for testing
• 0 to 2 usb wifi dongles (depending on Raspberry Pi model), to builtin wifi.
>

Schedule (uc)

Errors (uc)

Instructor Actions (uc)

Student Actions (uc)

Completion Standards (uc)

• (Application) Raspberry Pi boots and connects with static ip via wifi or ethernet

Bibliography (uc)

(gcc)

pub by Free Software Foundation, Inc.

http://www.gnu.org/software/gcc/