Vaibhav Bajpai | Blog

OpenWRT on TP Link TL WR703N: EUR. 20,99

04 January 2013


OpenWRT is an operating system primarily used on embedded devices to route network traffic. The main components are the Linux kernel, uClibc and BusyBox. All components have been optimized for size, to be small enough to fit the limited storage and memory available in home routers. OpenWRT is configured using a command-line interface, ash, or a web interface, LuCI. There are about 2000 optional software packages available for install via the opkg package management system.

Once the OpenWRT setup is complete, it should be possible to cherry-pick the components one wishes to install.

Planned Setup


The image is taken from the DD-WRT client bridge manual (0). The wireless access point connected to the modem is provided by the ISP. The plan is to run TP-Link TLWR703N as a wireless client. The client also should bridge the wireless interface and ethernet interface together, so that it can relay the traffic from the ethernet interface to the wireless interface and vice versa. The USB port on the router is going to be used to setup a Time Capsule. The router is also going to be a IPv6 tunnel endpoint and we will use stateless autoconfiguration to allocate the routed prefixes over the ethernet interface. This will allow all the hosts connecting over the ethernet interface of the router to receive a (psuedo-static) global-scope IPv6 address so that we can reach them from the outside world. We will also assign DNS names to the AAAA records using the nearlyfreespeech DNS service. This will allow us to backup our hosts from anywhere and everywhere, given we use miredo to get a IPv6 address at places we don’t get native IPv6.

Installing OpenWRT

Do not flash OpenWRT on a v1.7 firmware. The new bootloader revision disables the LAN port on boot (1). I fortunately got shipped with a v1.6 firmware. The default web interface is in chinese, but we only have to use it once during the flashing process.


Download the OpenWRT factory image for TP-Link TLWR703N from the bleeding edge trunk, codenamed Barrier Breaker. The bleeding edge version does not install the Luci webinterface by default. I have successfully flashed the 03-Jan-2013 nightly build. I am using the squashfs image to allow writes on a transparent overlay. This allows a failsafe mode to revert back to the squashfs image for recovery purposes. The default chinese configuration fails on longer filenames, therefore rename the image before flashing.

>> git clone WR703N/
[WR703N] >> mv openwrt-ar71xx-generic-tl-wr703n-v1-squashfs-factory.bin openwrt.bin


Start the flash process


IP address of the interface is Send an ICMP request.

>> ping

The telnet daemon is running on port 23. Login into the OpenWRT console

>> telnet
BusyBox v1.19.4 (2013-01-03 03:22:48 PST) built-in shell (ash)
Enter 'help' for a list of built-in commands.

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 BARRIER BREAKER (Bleeding Edge, r34996)
  * 1/2 oz Galliano         Pour all ingredients into
  * 4 oz cold Coffee        an irish coffee mug filled
  * 1 1/2 oz Dark Rum       with crushed ice. Stir.
  * 2 tsp. Creme de Cacao

dropbear by default does not accept connections. It has to be enabled

(openWRT) # passwd
>> ssh [email protected]

To revert back to this point at anytime from now:

(openWRT) # firstboot

If the console is also not accessible, then revert using the OpenWRT failsafe mode using the hardware RESET button (2). This assumes that the squashfs partition or the kernel is not broken (3).

Introspecting stock OpenWRT build

The snapshot runs linux kernel v3.6.11.

(openWRT) # uname -a
Linux OpenWrt 3.6.11 #1 Thu Jan 3 10:23:55 PST 2013 mips GNU/Linux

The interface lan and wireless interfaces wlan0/wlan1 are bridged together to br-lan.

[email protected]:~# uci show network

[email protected]:~# uci show wireless
[email protected][0]=wifi-iface
[email protected][0].device=radio0
[email protected][0].network=lan

Wireless is disabled by default.

(openWRT) # uci show wireless

IPv4 forwarding is enabled by default (ofcourse)

(openWRT) # cat /etc/sysctl.conf | grep forward

IPv6 is enabled by default.

(openWRT) # cat /etc/config/firewall | grep ipv6
#       option disable_ipv6     1

IPv6 forwarding …

IP Masquerading is enabled by default

(openWRT) # uci show firewall | grep masq
[email protected][1].masq=1 

ntp daemon is setup, and running by default in client mode.

(openWRT) # uci show ntp

DHCP requests are handled by dnsmasq. The daemon is running and allocates addresses to connected hosts on interface lan from -

(openWRT) # ps | grep dnsmasq
1012 nobody     952 S    /usr/sbin/dnsmasq -C /var/etc/dnsmasq.conf

(openWRT) # cat /etc/config/dhcp
config dhcp lan
        option interface        lan
        option start    100
        option limit    150
        option leasetime        12h

Installed packages:

(openWRT) # opkg list-installed  

The kernel is not part of the root filesystem, /. The root filesystem, / itself consists of /root and /overlay. /root is partitioned with the read-only squashfs filesystem, while /overlay is partitioned with writeable jffs2 filesystem. /overlay contains everything written after vanilla openWRT installation (4)

(openWRT) # df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                    1.3M    208.0K      1.1M  15% /
/dev/root                 1.5M      1.5M         0 100% /rom
tmpfs                    14.2M     60.0K     14.1M   0% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/mtdblock3            1.3M    208.0K      1.1M  15% /overlay
overlayfs:/overlay        1.3M    208.0K      1.1M  15% /

The device has 4M of flash and 32M of RAM. It appears I have 1.1M of flash and 14.1M of RAM at my disposal after stock openWRT installation.

Enable Wireless (Client Mode)

Enable wireless radio

(openWRT) # uci set [email protected][0].disabled=0
(openWRT) # uci commit wireless
(openWRT) # wifi
(openWRT) # ifconfig wlan0

Create an interface for the wireless station

(openWRT) # uci set network.wwan=interface
(openWRT) # uci set network.wwan.proto=dhcp
(openWRT) # uci commit network

Switch from bridged network to the newly created wireless interface

(openWRT) # uci set [email protected][0].network=wwan
(openWRT) # uci commit wireless

Switch from access point mode to station mode

(openWRT) # uci set [email protected][0].mode=sta
(openWRT) # uci commit wireless

Connect to an access point. Supply your $SSID and $SECRET_KEY. I am using channel 6 and WPA2-PSK encryption for my access point.

(openWRT) # uci set
(openWRT) # uci set [email protected][0].ssid=$SSID
(openWRT) # uci set [email protected][0].encryption=psk
(openWRT) # uci set [email protected][0].key=$SECRET_KEY
(openWRT) # uci commit wireless

Apply the changes

(openWRT) # wifi down; wifi

If the the resource is busy, a reboot will fix it.

(openWRT) # reboot

Test Internet connectivity

(openWRT) # ping -I wlan0
(openWRT) # ping -I wlan0

It’s better to assign a static IP address to the wireless interface to allow easy remote access. My access point is at

(openWRT) # uci set network.wwan.proto=static
(openWRT) # uci set network.wwan.ipaddr=
(openWRT) # uci set network.wwan.netmask= 
(openWRT) # uci set network.wwan.gateway=
(openWRT) # uci set network.wwan.broadcast=
(openWRT) # uci set network.wwan.dns=
(openWRT) # uci commit network

Restart the Network

(openWRT) # /etc/init.d/network restart

If the the resource is busy, a reboot will fix it.

Update the Packages

opkg is the OpenWRT package management system.

(openWRT) # opkg update

If opkg currently runs out of space, it will not remove the files it was installing. Run this custom script (7) in order recover the space by removing these files and the installed dependencies.

>> git clone opkgclean
>> scp opkgclean/ [email protected]:/tmp
(openWRT) # /tmp/ $PACKAGE
(openWRT) # reboot

The destination for packages installed via opkg can be altered as well. This might be useful when connecting a USB drive to the USB port and installing packages there. Although the cleanest way is to perform a pivot overlay, which mounts the whole /overlay to an external USB disk. We will do this later.

Create a Pseudobridge with LAN interface

The atheros wireless drivers do not support bridging the wireless network with the LAN interface when the wireless is set in station mode. As a result, relayd package is used to create pseudobridge by relaying the DHCP and broadcast traffic.

Install relayd:

(openWRT) # opkg install relayd
(openWRT) # /etc/init.d/relayd enable 

Declare a relay interface

(openWRT) # uci set network.stabridge=interface
(openWRT) # uci set network.stabridge.proto=relay
(openWRT) # uci set"lan wwan"
(openWRT) # uci commit network

Disable the local DHCP server on the router. The DHCP requests from the LAN network will be relayed to the access point and responded back.

(openWRT) # uci set dhcp.lan.ignore=1
(openWRT) # uci commit dhcp

Allow forwarded traffic within the LAN zone. Forwarded traffic is disabled by default in vanilla OpenWRT installations. Packets forwarded by relayd are managed by the internal routing system, and hence are affected by the firewall policies.

(openWRT) # uci set [email protected][0].forward=ACCEPT
(openWRT) # uci set [email protected][0].network="lan wwan" 
(openWRT) # uci commit firewall

Set OpenWRT router’ IP address in relayd configuration. This will enable clients connecting to OpenWRT over the LAN segment to ping and ssh back into the OpenWRT router. This is why it was essential to assign a static IP on the wireless interface of the OpenWRT router when setting it to station mode.

(openWRT) # uci set network.stabridge.ipaddr=
(openWRT) # uci commit network

Apply the changes

(openWRT) # /etc/init.d/dnsmasq restart
(openWRT) # /etc/init.d/firewall restart
(openWRT) # wifi down; wifi

If the resource is busy, a reboot will fix it.

Add USB Support

Confirm basic USB support

(openWRT) # opkg list-installed | grep usb
kmod-ledtrig-usbdev - 3.6.11-1
kmod-usb-core - 3.6.11-1
kmod-usb-ohci - 3.6.11-1
kmod-usb2 - 3.6.11-1

Connect a USB storage device and check the kernel message buffer

(openWRT) # dmesg
[...] usb 1-1: new high-speed USB device number 3 using ehci-platform

Install package to support USB mass storage devices.

(openWRT) # opkg install kmod-usb-storage
(openWRT) # dmesg
[...] SCSI subsystem initialized
[...] Initializing USB Mass Storage driver...
[...] scsi0 : usb-storage 1-1:1.0
[...] usbcore: registered new interface driver usb-storage
[...] USB Mass Storage support registered.
[...] scsi 0:0:0:0: Direct-Access SanDisk Cruzer Blade 1.03 PQ: 0 ANSI: 2
[...] sd 0:0:0:0: [sda] 15633408 512-byte logical blocks: (8.00 GB/7.45 GiB)
[...] sd 0:0:0:0: [sda] Write Protect is off
[...] sd 0:0:0:0: [sda] Mode Sense: 03 00 00 00
[...] sd 0:0:0:0: [sda] No Caching mode page present
[...] sd 0:0:0:0: [sda] Assuming drive cache: write through
[...] sd 0:0:0:0: [sda] No Caching mode page present
[...] sd 0:0:0:0: [sda] Assuming drive cache: write through
[...] sda: sda1 sda2
[...] sd 0:0:0:0: [sda] No Caching mode page present
[...] sd 0:0:0:0: [sda] Assuming drive cache: write through
[...] sd 0:0:0:0: [sda] Attached SCSI removable disk

Install package to support mounting block devices.

(openWRT) # opkg install block-mount

The package is required to setup a fstab configuration.

Pivot-Overlay on a USB disk

The available disk space on /overlay is now less than a 1M. It is best to pivot the /overlay to a USB disk and make all the writes there.

Add ext4 filesystem support

(openWRT) # opkg install kmod-fs-ext4

kmod-fs-ext4 also supports mounting ext2 and ext3 partitions.

Add generic SCSI support. Linux kernel 2.6.30 and later uses the SCSI devices to link any additional storage media

(openWRT) # opkg install kmod-scsi-generic

Connect and manually mount the USB storage device.

(openWRT) # umount /dev/sda1
(openWRT) # mkdir -p /mnt/overlay
(openWRT) # mount -t ext4 /dev/sda1 /mnt/overlay -o rw,sync
(openWRT) # df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/sda1               967.5M     17.2M    901.1M   2% /mnt/overlay 

Copy the current /overlay to this mount point.

(openWRT) # tar -C /overlay -cvf - . | tar -C /mnt/overlay -xf -
(openWRT) # umount /mnt/overlay

Clean the current fstab configuration.

The fstab configuration is disabled by default. However, hotpluggable automounting and autoswapping behavior are already setup in the configuration. Example configuration for /home and swap are defined by default. Delete these examples to let them not use the mounted block device for /home and swapping purposes. The examples can always be brought back later from (5)

(openWRT) # /etc/init.d/fstab stop
(openWRT) # uci delete [email protected][0]
(openWRT) # uci delete [email protected][0]
(openWRT) # uci show fstab
(openWRT) # uci commit fstab

It is better to use UUID for devices over kernel name descriptors. The order of the name descriptors can change on reboot. To list the UUID of connected devices.

(openWRT) blkid
/dev/mtdblock2: TYPE="squashfs"
/dev/sda1: LABEL="EFI" UUID="70D6-1701" TYPE="vfat"
/dev/sda2: UUID="9938e96e-475b-3287-a05a-fc30d0b7a832" LABEL="USB" TYPE="hfsplus"
/dev/sdb1: UUID="7b8ab852-f247-48ca-b0d7-99dfd690b633" TYPE="ext4"

However, it appears busybox does not support mounting block devices by label or UUID. A utility, mount-utils (6) available in the package manager allows one to manually mount using a UUID, however it cannot be used by the init scripts at boot time.

Configure the pivot overlay in fstab

(openWRT) # /etc/init.d/fstab stop
(openWRT) # uci add fstab mount
(openWRT) # uci set [email protected][0].target=/overlay
(openWRT) # uci set [email protected][0].device=/dev/sda1
(openWRT) # uci set [email protected][0].fstype=ext4
(openWRT) # uci set [email protected][0].options=rw,sync
(openWRT) # uci set [email protected][0].enabled=1
(openWRT) # uci set [email protected][0].enabled_fsck=0
(openWRT) # uci show fstab
[email protected][0]=mount
[email protected][0].target=/overlay
[email protected][0].device=/dev/sda1
[email protected][0].fstype=ext4
[email protected][0].options=rw,sync
[email protected][0].enabled=1
[email protected][0].enabled_fsck=0
(openWRT) # uci commit fstab

Force opkg installation of packages bigger than /rom

(openWRT) # echo option force_space >> /etc/opkg.conf

Make the settings effective on reboot

(openWRT) # /etc/init.d/fstab enable
(openWRT) # reboot

Confirm the changes.

(openWRT) # df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                  967.5M     18.6M    899.7M   2% /
/dev/root                 1.5M      1.5M         0 100% /rom
tmpfs                    14.2M     84.0K     14.1M   1% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sda1               967.5M     18.6M    899.7M   2% /overlay
overlayfs:/overlay      967.5M     18.6M    899.7M   2% /

Good to have some breathing space! It’s currently unclear to me if a sysupgrade needs to be handled any differently now. I will try to avoid it until I am sure.

Setup Time Capsule

The router provides only 1 USB port, which is now used by the USB disk running our /overlay. A USB hub can surely add more ports, but the hub needs to be powered from an external power source to be suffice needs.

Install HFS+ filesystem support.

(openWRT) # opkg install kmod-fs-hfsplus

The storage devices prepared by the Disk Utility on Mac OS X usually contain a GUID partition table (as opposed to a MBR partition table). Fortunately, GUID partition table support is avaiable in the kernel of this OpenWRT nightly build. In addition, an hfsprogs utility is required to write to HFS+ drives that have journaling enabled. Without this utility, the drive will be mounted only in read-only mode. It appears hfsprogs is not currently available through the opkg package manager. It sure can be cross-compiled and bundled as package, but I am lazy to try it at this point.

Disable HFS+ Journaling in your Time Capsule. Press the Option Key when clicking the File menu.


Manually mount the USB storage device.

(openWRT) # mkdir -p /mnt/tm
(openWRT) # mount -t hfsplus /dev/sdb2 /mnt/tm -o rw,sync
(openWRT) # df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/sdb2               465.4G    387.4M    465.1G   0% /mnt/tm
(openWRT) # umount /mnt/tm

Configure for automount on boot.

(openWRT) # /etc/init.d/fstab stop
(openWRT) # uci add fstab mount
(openWRT) # uci set [email protected][1].device=/dev/sdb2
(openWRT) # uci set [email protected][1].options=rw,sync
(openWRT) # uci set [email protected][1].enabled_fsck=0
(openWRT) # uci set [email protected][1].enabled=1
(openWRT) # uci set [email protected][1].target=/mnt/tm
(openWRT) # uci show fstab
[email protected][1]=mount
[email protected][1].device=/dev/sdb2
[email protected][1].options=rw,sync
[email protected][1].enabled_fsck=0
[email protected][1].enabled=1
[email protected][1].target=/mnt/tm
(openWRT) # uci commit fstab

Make the settings effective on reboot

(openWRT) # /etc/init.d/fstab enable
(openWRT) # reboot

Both the disk mounted properly.

(openWRT) # df -h
Filesystem                Size      Used Available Use% Mounted on
rootfs                  967.5M     18.6M    899.7M   2% /
/dev/root                 1.5M      1.5M         0 100% /rom
tmpfs                    14.2M     84.0K     14.1M   1% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sda1               967.5M     18.6M    899.7M   2% /overlay
overlayfs:/overlay      967.5M     18.6M    899.7M   2% /
/dev/sdb2               465.4G    387.4M    465.1G   0% /mnt/tm

Setup netatalk

(openWRT) # opkg install netatalk

Add a new user for Time Capsule

(openWRT) # vim /etc/passwd

Set a password for the user

(openWRT) # passwd vbajpai

Define a Time Capsule share

(openWRT) # vim /etc/netatalk/AppleVolumes.default 
/mnt/tm "Time Capsule" allow:vbajpai cnidscheme:dbd options:usedots,upriv,tm

Start the AFP daemon

(openWRT) # /etc/init.d/afpd start

Enable AFP daemon on boot

(openWRT) # /etc/init.d/afpd enable

Change ownership for Time Capsule

(openWRT) # chown -R vbajpai:root /mnt/tm

Mount Time Capsule on Mac OS X

>> open afp://openwrt


Setup Time Machine in Preferences


On a “something wrong with the volume’s cnid db” response, the Time Capsule is mounted in read-only mode. To recover:

>> rm -rf .AppleDB/ .AppleDouble/

This only happens to me whenever I reboot the router.

Finally the backup has started:


Secure Remote Acess.

Use Public-Key Authentication

>> scp ~/.ssh/ [email protected]:/tmp
(openWRT) # cat /tmp/ >> /etc/dropbear/authorized_keys
(openWRT) # chmod 600 /etc/dropbear/authorized_keys

Disable Password-based logins.

(openWRT) # uci set [email protected][0].PasswordAuth=off
(openWRT) # uci commit dropbear

Setup a SSH config on the clients

>> vim ~/.ssh/config
Host openwrt
  Host openwrt
  Port 22
  User root

We will later update it with global-scope IPv6 addresses.

Enable IPv6 Support

Install IPv6 kernel module

(openWRT) # opkg install kmod-ipv6
(openWRT) # ifconfig wlan0
inet6 addr: fe80::ee17:2fff:fea7:f5d7/64 Scope:Link

Enable IPv6 forwarding

(openWRT) # vim /etc/sysctl.conf
(openWRT) # reboot

Test Link-Local Connectivity

(openWRT) # ping6 -I wlan0 fe80::21b:77ff:fece:8bac

Obtain IPv6 on the OpenWRT router, by establishing a dyanamic 6-in-4 tunnel offered by Hurricane Electric (8). A free registration and regular tunnel creation process needs to be done on the website.

(openWRT) # opkg install 6in4
(openWRT) # uci set network.henet=interface
(openWRT) # uci set network.henet.proto=6in4
(openWRT) # uci set network.henet.peeraddr=216.xx.xx.xx
(openWRT) # uci set network.henet.ip6addr='2001:xxx:1f14:xxx::2/64'

Set the HE credentials in the interface configuration. The password is a MD5 hash of password and can be generated using md5sum

(openWRT) # echo -n $PASSWORD | md5sum
(openWRT) # uci set network.henet.tunnelid=19xxxx
(openWRT) # uci set network.henet.username=tb50xxxxxxxxxxxxxxxxx
(openWRT) # uci set network.henet.password=61067befxxxxxxxxxxxxxxxxxxxxx
(openWRT) # uci commit network

Apply IPv6 firewall rules to the tunnel interface by adding it to the wan zone

(openWRT) # uci set [email protected][1].network='wan henet'
(openWRT) # uci commit firewall

Apply the changes

(openWRT) # /etc/init.d/network restart
(openWRT) # /etc/init.d/firewall restart

Check the new interface

(openWRT) # ifconfig 
6in4-henet Link encap:IPv6-in-IPv4  
           inet6 addr: fe80::c0a8:32/128 Scope:Link
           inet6 addr: 2001:xxx:1f14:xxx::2/64 Scope:Global
           UP POINTOPOINT RUNNING NOARP  MTU:1480  Metric:1
           RX packets:2 errors:0 dropped:0 overruns:0 frame:0
           TX packets:2 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:208 (208.0 B)  TX bytes:208 (208.0 B)

Ping to the remote tunnel endpoint

(openWRT) # ping6 2001:xxx:1f14:xxx::1
64 bytes from 2001:xxx:1f14:xxx::1: seq=0 ttl=64 time=28.648 ms

Ping other endpoints

(openWRT) # ping6
64 bytes from 2a00:1450:4008:c01::69: seq=0 ttl=55 time=48.080 ms

Propagate IPv6 subnet to LAN

Assign an address out of the routed IPv6 subnet forwarded by HE to the lan facing interface of the OpenWRT router.

(openWRT) # uci set network.lan.ip6addr=2001:xxx:1f15:xx::/64
(openWRT) # uci commit network
(openWRT) # /etc/init.d/network restart
(openWRT) # ifconfig br-lan
inet6 addr: 2001:xxx:1f15:xxx::/64 Scope:Global

Spread IPv6 in the internal LAN using radvd (9), which sends link-local advertisements of IPv6 routing prefixes using the Neighbor Discovery Protocol.

(openWRT) # opkg install radvd

Configure the IPv6 routing prefixes to be advertised

(openWRT) # vim /etc/config/radvd
config interface
        option interface        'lan'
        option AdvSendAdvert    1
        option AdvManagedFlag   0
        option AdvOtherConfigFlag 0
        list client             ''
        option ignore           0

config prefix
        option interface        'lan'
        list prefix             '2001:xxx:1f15:xxx::/64'
        option AdvOnLink        1
        option AdvAutonomous    1
        option AdvRouterAddr    0
        option ignore           0

Activate radvd

(openWRT) # /etc/init.d/radvd enable
(openWRT) # /etc/init.d/radvd start

Test IPv6 connectivity from within LAN hosts.

>> p6 2001:xxx:1f14:xxx::2
16 bytes from 2001:xxx:1f14:xxx::2, icmp_seq=0 hlim=64 time=5.075 ms

>> p6
16 bytes from 2a00:1450:4008:c01::6a, icmp_seq=0 hlim=54 time=46.368 ms 

The IPv6 addresses on the host are generated by concatenating the host MAC address with the static routed prefix. Unless privacy extensions are enabled, the IPv6 addresses generated is slated to remain static (globally) static for a host, which can bring good and bad news.

Replace ash with bash

bash provides more capabilities over ash

(openWRT) # opkg update
(openWRT) # opkg install bash
(openWRT) # vi /etc/passwd
- root:x:0:0:root:/root:/bin/ash
+ root:x:0:0:root:/root:/bin/bash

You may have to exit and ssh back again for changes to take effect.

Replace bash with zsh

I personally prefer zsh over bash.

(openWRT) # opkg update
(openWRT) # opkg install zsh
(openWRT) # vi /etc/passwd
- root:x:0:0:root:/root:/bin/bash
+ root:x:0:0:root:/root:/bin/zsh

You may have to exit and ssh back again for changes to take effect.

Replace dropbear with openssh

Switch dropbear running instance to a different port

(openWRT) # uci set [email protected][0].Port=2222
(openWRT) # uci commit dropbear
(openWRT) # /etc/init.d/dropbear restart

Exit and login back

(openWRT) # exit
>> ssh openwrt -p 2222

Install openssh-server

(openWRT) # opkg install openssh-server

Start openssh-server

(openWRT) # /etc/init.d/sshd enable
(openWRT) # /etc/init.d/sshd start

Exit and login back

(openWRT) # exit
>> ssh openwrt

Reset drobpear ssh client symlinks

(openWRT) # ln -s /usr/sbin/dropbear /usr/sbin/ssh
(openWRT) # ln -s /usr/sbin/dropbear /usr/sbin/scp
(openWRT) # rm /usr/bin/ssh
(openWRT) # rm /usr/bin/scp

Install openssh-client

(openWRT) # opkg install openssh-client

You can now disable dropbear to save some RAM

Supercharge /tmp

The tmpfs partition is restricted to 50% of the RAM. It would be great to move the files in /tmp to swap as soon as applications need more RAM for themselves. The swap disabled by default

(openWRT) # free
             total         used         free       shared      buffers
Mem:         29016        27920         1096            0         4560
-/+ buffers:              23360         5656
Swap:            0            0            0

Install swap-utils

(openWRT) # opkg install swap-utils

Mount swap to a USB partition.

>> sudo mkswap /dev/sdc1
(openWRT) # uci add fstab swap
(openWRT) # uci set [email protected][0].device=/dev/sdc1
(openWRT) # uci set [email protected][0].enabled=1
(openWRT) # uci commit fstab
(openWRT) # reboot
(openWRT) # free
             total         used         free       shared      buffers
Mem:         29016        27920         1096            0         4560
-/+ buffers:              23360         5656
Swap:      1049460            0      1049460

Remove the 50% limit on /tmp and set it to swap size

(openWRT) # uci add fstab mount
(openWRT) # uci set fstab.mount[2].target=/tmp
(openWRT) # uci set [email protected][2].device=tmpfs
(openWRT) # uci set [email protected][2].fstype=tmpfs
(openWRT) # uci set [email protected][2].options=remount,rw,nosuid,nodev,noatime,size=1024M
(openWRT) # uci set [email protected][2].enabled_fsck=0
(openWRT) # uci set [email protected][2].enabled=1
(openWRT) # uci commit fstab

Change the swapiness value to make kernel avoid swapping as much as possible

(openWRT) # sysctl -w vm.swappiness=5
(openWRT) # reboot

The mount point /tmp can also instead be moved to a partition on a USB.

>> sudo mkfs -t ext3 /dev/sdc2
(openWRT) # uci add fstab mount 
(openWRT) # uci set [email protected][3].target=/mnt/tmp
(openWRT) # uci set [email protected][3].device=/dev/sdc2
(openWRT) # uci set [email protected][3].fstype=ext3
(openWRT) # uci set [email protected][3].options=rw,noatime
(openWRT) # uci set [email protected][3].enabled=1
(openWRT) # uci set [email protected][3].enabled_fsck=1

This creates a mount point to put /tmp

\var is set a symbolic link to \tmp by default. This means, opkg caches are flushed on every reboot, and an opkg update is required.

>> sudo mkfs -t ext4 /dev/sdc3
(openWRT) # uci add fstab mount
(openWRT) # uci set [email protected][4].device=/dev/sdc3
(openWRT) # uci set [email protected][4].options=rw,sync
(openWRT) # uci set [email protected][4].enabled_fsck=0
(openWRT) # uci set [email protected][4].enabled=1
(openWRT) # uci set [email protected][4].target=/mnt/var
(openWRT) # uci commit fstab 
(openWRT) # reboot

Create a new symbolic link

(openWRT) # rm /var
(openWRT) # ln -s /mnt/var /var

The package manager caches will now remain up to date and survive reboots.

Create a separate user

Connect a USB drive for /home

(openWRT) # uci add fstab mount
(openWRT) # uci set [email protected][5].device=/dev/sdc4
(openWRT) # uci set [email protected][5].options=rw,sync
(openWRT) # uci set [email protected][5].enabled_fsck=0
(openWRT) # uci set [email protected][5].enabled=1
(openWRT) # uci set [email protected][5].target=/mnt/home
(openWRT) # uci commit fstab 
(openWRT) # reboot

Stop using root

(openWRT) # mkdir -p /mnt/home/vbajpai
(openWRT) # vi /etc/passwd
(openWRT) # vi /etc/group

Give yourself sudo rights

(openWRT) # opkg install sudo
(openWRT) # visudo
root ALL=(ALL) ALL
vbajpai ALL=(ALL) ALL

Assign setuid bits on certain busybox applets

(openWRT) # cp /bin/busybox /bin/busybox-setuid
(openWRT) # chmod u+s /bin/busybox-setuid
(openWRT) # rm /usr/bin/crontab
(openWRT) # ln -s /bin/busybox-setuid /usr/bin/crontab
(openWRT) # rm /bin/ping /bin/ping6
(openWRT) # ln -s /bin/busybox-setuid /bin/ping
(openWRT) # ln -s /bin/busybox-setuid /bin/ping6
(openWRT) # rm /usr/bin/traceroute
(openWRT) # ln -s /bin/busybox-setuid /usr/bin/traceroute
(openWRT) # opkg install iputils-traceroute6
(openWRT) # chmod u+s /usr/bin/traceroute6

Use public-key authentication

(openWRT) # cp /etc/dropbear/authorized_keys ~/.ssh/
(openWRT) # exit
>> ssh openwrt

Fetch your dotfiles

(openWRT) $ opkg install git
(openWRT) $ sudo ln -s /usr/bin/git /usr/libexec/git-core/git
(openWRT) $ git clone [email protected]:USER/dotfiles.git .dotfiles

Set a better TERM

(openWRT) $ export TERM=xterm-color

This is will be required for vim and tmux

Install development tools

This is my personal choice of tools

(openWRT) $ sudo opkg install binutils
(openWRT) $ sudo opkg install vim
(openWRT) $ sudo opkg install tmux

Some people would prefer to install emacs

Enable USB Tethering support

The router can be used as bridge to connect resource constrained low-powered IoT devices to the IPv6 world over 802.15.4 wireless protocol. I have a Atmel AVR RZ USBstick that has a 802.15.4 radio and can decode 6LowPAN packets and transfer them to the router over its USB interface. The USB interface needs to emulate as a network device using rndis.

(openWRT) $ dmesg
[...] usb 1-1.1: new full-speed USB device number 9 using ehci-platform

Install rndis support.

(openWRT) $ sudo opkg install kmod-usb-net-rndis

You’re now good to go.

Setup Print Server

Install cups

# opkg install cups

Change the spool directory. Point it to a location which has higher disk space.

# vim /etc/cups/cupsd.conf
- RequestRoot /var/cups
+ RequestRoot /mnt/var/cups

Start cups

# /etc/init.d/cupsd enable
# /etc/init.d/cupsd start

The web interface should now be available at port 631

IPv6 Relay

I recently started receiving native IPv6 connectivity from my ISP. My ISP provides me a /64 prefix over a logical link. However, no routed subnet prefix is provided. In order to provide IPv6 connectivity to some of my downstream hosts, I had to relay IPv6 router advertisements from my CPE through my OpenWrt router. I used 6relayd for this:

# opkg install 6relayd

The configurations were set as follows:

# cat /etc/config/6relayd
config server examplerelay
        option master   'wwan'
        option network  'lan'
        option rd       'relay'
        option dhcpv6   'relay'
        option ndp      'relay'

Restart and enable 6relayd:

# /etc/init.d/6relayd start
# /etc/init.d/6relayd enable

(0) DD-WRT: Client Bridged →
(1) TLWR703N: Warnings →
(2) TLWR703N: Failsafe Mode →
(3) OpenWRT Debricking Guide →
(4) OpenWRT: Flash Layout →
(5) OpenWRT: fstab Configuration →
(6) OpenWRT Forum: mount-utils →
(7) OpenWRT: opkg Package Manager →
(8) Hurricane Electric →
(9) radvd →

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