The TP-Link TL-MR3420 is a Fast Ethernet b/g/n 300M (two 3 dBi omni-antennas) wireless router with USB 2.0.
The TP-Link TL-MR3220 is a Fast Ethernet b/g/n Lite-N 150M (one 5 dBi omni-antennae) wireless router with USB 2.0.
The TP-Link TL-WR842ND is a Fast Ethernet b/g/n 300M (two 5 dBi omni-antennas) wireless router with USB 2.0.
The TP-Link TL-WR841ND v7 is a Fast Ethernet b/g/n 300M (two 3 dBi omni-antennas) wireless router without USB 2.0, but has a header in place.

Model Version	FCC ID	OpenWrt Version Supported	Model Specific Notes
MR3220 v1	TE7MR3220	AA 12.09b (r24439)	-
MR3220 v1.2		AA 12.09b (r27340)	Success Success Spanish 3G
MR3220 v2	Aug-2012	WiP	TL-AP121 Success
MR3220 v2.1	???later	???ar71xx	Success
MR3420 v1.0	TE7MR3420	Backfire 10.03.1 (r23138)	-
MR3420 v1.1		Backfire 10.03.1 (r23138)	Success
MR3420 v1.2		Backfire 10.03.1 (r23138)	Success
MR3420 v2	Aug-2012	Unsupported	TL-AP121
MR3420 v2.1	Dec-2012	???	???
WR841ND v7.1	-	AA 12.09b (r23134)	TL-WR841ND
WR841ND v7.2	-	AA 12.09b (r30310)	-
WR842ND v1.0	TE7WR842ND	AA 12.09b (r30508)	TL-WR842ND

The failsafe function is not working at launch time, serial is also unfriendly: Stick to trunk. More...

Snapshot images are always risky. Check the forum discussion for latest opinions on available images.

Has known bugs, read carefully: #12135, #12143.

TL-MR3420,
TL-WR841ND v7 &
TL-WR842ND: Atheros AR9287 wireless chip. Single-band, 2x2 MIMO configuration

TL-MR3220: Atheros AR9285 wireless chip. Single-stream (no MIMO, Lite-N)

• TP-Link TL-MR3420 and TL-MR3220 howto build
• TP-Link TL-MR3420, TL-MR3220 and TL-WR842MD howto 3G

This section details what is required to install and upgrade OpenWrt. First we link to software that you should download before you start reading the instructions on how to install.

Please double-check if the image revision you are downloading is newer than supported by the "Model Version" of your router.

• Download a Install Image from this group if is the first flash from OEM firmware:

• Download a Upgrade Image from this group for already installed OpenWRT systems instead:

• Download PuTTY and PSCP tools for SSH connection even if you don't know what SSH is.
• Download latest original firmware for your router MR3420/MR3220/WR842ND just in case upgrade goes wrong and need it to recover Internet access.

OEM easy installation

This section deals with how you install OpenWrt from a device freshly opened. Plus the steps required such as reset to factory defaults if the device has already been configured

Note: Reset router to factory defaults if it has been previously configured.

Note: Newer TP-Link retail firmwares (confirmed on v2.4 devices, but definitely not on v2.0) include a crude mechanism to prevent you uploading unsuitable firmware. It does this by checking the filename, so you may need to rename the *-factory.bin file to the name of a TP-Link retail firmware file. e.g. wr741nv1_en_3_12_4_up(100910).bin (not necessary with firmware V4_120320)

• Browse to your router at http://192.168.1.1/ or test with TP-LINK Simulator first. (Version 4.20 uses http://192.168.0.1 out of the box.)
• Login with user name: admin password: admin
• Use left navigation panel and go to System Tools
• Navigate to - Factory Defaults and click on Restore if it has been previously configured.
  • Confirm the pop-up dialog.
• Then navigate to - Firmware Upgrade
• Upload previously chosen -factory.bin file to router
• Click on Upgrade button and wait for it to reboot
• Do NOT turn off the power during upgrade
• Wait about 120 seconds to start up, see SYS LED activity.
• If the router's IP (192.168.1.1) doesn't repond to ping, try clear ARP cache on your machine

  arp -d

• Don't clear your browser cache! Please report here what you installed, if do http://192.168.1.1/ work anyway and which link let you get in. Successful ones have removed. This only happen once, so your input is important.

192.168.1.1	Alternate links that theoretically should work
Gargoyle	http://192.168.1.1/login.sh	https://192.168.1.1/login.sh
LuCI	http://192.168.1.1/index.html	http://192.168.1.1/cgi-bin/luci
X-Wrt	http://192.168.1.1/index.html	http://192.168.1.1/cgi-bin/webif/info.sh

• Clear your browser cache if you are sure some web interface is installed, but can't access to http://192.168.1.1/
• Set a root password
  • Browse to http://192.168.1.1/ if LuCI, X-Wrt or Gargoyle web interface is installed.
    • Only for Gargoyle login with defaults user name: root password: password
    • After password has been setup login with user name: root password: previusly entered
  • telnet 192.168.1.1
    • Type:

      passwd root

    • Enter your new password twice.
• Once password has been setup Telnet is no longer available, use SSH instead to connect.
  • ssh root@192.168.1.1
  • PuTTY SSH

Install the OpenWrt image using "Firmware Upgrade" from the orginal firmware.

1. Download openwrt-ar71xx-generic-tl-mr3420-v1-squashfs-factory.bin
2. Connect your pc via serial interface.
3. use a tftpd server name the the firmware code.bin and set your ip to 192.168.1.27
4. power on the router, and type tpl if "Autoboot in .." occurs (type fast!)
5. if it works you now should see: ar7100>
6. Now you should type the following:

ar7100> erase 0x9f020000 +0x3c0000 ar7100> tftpboot 0x81000000 code.bin ar7100> cp.b 0x81000000 0x9f020000 0x3c0000 ar7100> bootm 0x9f020000

(source: http://eko.one.pl/?p=openwrt-mr3420)

The following procedure was tested with a TL-WR842ND.

Enter failsafe mode:

1. remove the power plug from the router
2. press and hold the RESET button
3. insert the power plug
4. release the RESET button

Some seconds later no LED besides the one for USB (and maybe for attached ethernet ports) should be lit.

The device now uses the IP 192.168.1.86. It repeatedly tries to download a file named wr842ndv1_tp_recovery.bin from a tftpd server with the IP 192.168.1.66. You can verify these continuous requests with a network sniffer (e.g. tcpdump or wireshark).

The following steps will serve an openwrt fimrware image to the device:

1. download an appropriate firmware file (e.g. openwrt-ar71xx-generic-tl-wr842n-v1-squashfs-factory.bin)
2. create a symlink or rename the file: ln -s openwrt-ar71xx-generic-tl-wr842n-v1-squashfs-factory.bin wr842ndv1_tp_recovery.bin
3. configure the static IP 192.168.1.66 for your local ethernet interface
4. connect your computer to one of the LAN ports of the router
5. install a tftpd server (e.g. atftpd)
6. run the tftpd server and let it serve the directory that contains the above firmware image: atftpd –no-fork –daemon FIRMWARE_DIRECTORY
7. the router immediately starts to download the firmware image
8. after some time you will see all LEDs flashing once followed by a normal restart of the router

Front:

Back:

Board:

Photo source
More photos: 1, 2, 3

Front:

Back:

Board:

Photo source
More photos: 1, 2, 3, 4

Pin 1 is clearly marked on the board.

To get the serial connection work reliably, you have to connect a 10k pullup resistor between the TX and the 3.3V pin. This is because the TX pin is connected to a voltage divider (2x5.6k) and a capacitor is put between the real pin and the TX connector. ³⁾

Now connect a serial hack adapter (DKU-5, CA-42 or similar containing the PL-2303 chip) and away you go!
The right settings for accessing the serial console are as follows:

Bits per second: 115200
Data bits: 8
Stop bits: 1
Parity: None
Flow control: None

Password to get into uboot prompt is tpl
Password to get root login is 5up

Since this part is identical for all devices, see Basic configuration.

Note: (TP-Link MR4320 v1.2) In case the vlan switch configuration is not created automagically (⇐ 10.03.1) and there is eth0 and eth1 after bootup change /etc/config/network to reflect the vlan setup by adding the lines below. Also replace the 'option ifname "ethX"' accordingly (eth0.1, eth0.2). The proper ethernet port layout has still to be confimed.

config switch eth0                   
      	option reset 1                     
      	option enable_vlan 1             
                                     
config switch_vlan
        option device eth0          
        option vlan 1               
        option ports "0t 1 2 3 4" 
                                                                      
config switch_vlan         
        option device eth0       
      	option vlan 2            
      	option ports "0t 5"

In MR3220 v1.2 is:

config 'switch'
	option 'name' 'eth0'
	option 'reset' '1'
	option 'enable_vlan' '1'
      
config 'switch_vlan'
	option 'device' 'eth0'
	option 'vlan' '1'
	option 'ports' '0 1 2 3 4'

Since this is the same for all TP-LINK products, see TP-LINK firmware features.

Failsafe is a quite popular feature, of this router, thats lets you recover instantly from a misconfiguration above.

Use the QSS button instead of reset button, everything else is identical to generic failsafe document.

Failsafe may not work in Backfire before r29661, so it's confirmed to not work at Backfire 10.03.1 launch (r29592). Be extremely cautious on what you're doing or go directly to serial recovery.

Note for MR-3220 running on 12.09-rc1 (r34185): I did not get any UDP packets to port 4919 as promised either when connected to LAN or WAN, however repeatedly pushing the front button made the router to enter the failsafe mode, which allowed me to gain again access to the router. The problem almost bricking my router was in my network configuration, for some reason setting a fixed MAC address for a bridge caused the router to hang at /etc/init./network start.

To connect stuff to the USB port, please see Connect stuff to the USB port.

a custom image with ipv6 support: radvd, wide-dhcpv6, 3g stick support, made for RCS-RDS Fiberlink dual stack PPPoE service, but should be okay for static wan settings on other ISPs: http://www.ip6.ro/firmware/mr3420/