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title: OpenWrt on the DG834Gv4 modem router
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tags: [openwrt, modem, router, backdoor]
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updated: 2018-04-19 18:00
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description: Installing OpenWrt on the DG834Gv4 modem router
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---
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# Overview
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The [DG834Gv4](https://wikidevi.com/wiki/Netgear_DG834Gv4) is an old
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*Netgear* WiFi modem/router and has been my first wireless access
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point. Years have passed and this hardware shows signs
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of its age. It is compliant to
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[802.11 b/g](https://en.wikipedia.org/wiki/IEEE_802.11#802.11g) only and
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has 100 Mbps ethernet ports .
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Also, when using it as a DSL modem, it sometimes disconnects
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because of the heat it generates. It was time to decommission it.
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In the meantime someone discovered a *nice*
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[backdoor](https://github.com/elvanderb/TCP-32764)
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[feature](https://wikidevi.com/wiki/TCP-32764) in a series of
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modem/routers, including the DG834Gv4. One more reason not to use it *as-is*.
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*After the router collected some dust*, I evaluated some options such as
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installing OpenWrt or the [DGTeam](http://www.dgteam-mirror.talktalk.net/Home.html) firmwares.
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I went with the DGTeam firmware at first because it had modem support. This
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meant I could use it as a spare modem.
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A few weeks ago, however, I tried installing OpenWrt and it wasn't so straight
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forward as I thought.
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# Steps
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- [Follow the instuctions reported on the wiki](https://openwrt.org/toh/netgear/dg834g.v4?s[]=dg834gv4)
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but instead of getting Chaos Calamer get
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[Attitude Adjustment](https://archive.openwrt.org/attitude_adjustment/12.09/brcm63xx/generic/openwrt-96348GW-10-generic-squashfs-cfe.bin).
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Use `nftp.c` to flash the image on it. This will work even of you brick the
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router.
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The reason to select such an old image is because of the insufficient free
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RAM available once the important services start up. Even with Attitude
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Adjustment you'll run out of memory easily. I also tried using older versions
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of OpenWrt without success.
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- Go to [http://192.168.1.1](http://192.168.1.1) and change the root password via the *LuCI* web interface.
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This will also enable the SSH daemon.
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- Login via SSH (`ssh root@192.168.1.1`) and run the following to remove
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the web interface.
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/etc/init.d/uhttpd stop
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/etc/init.d/uhttpd disable
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# repeat the following until no more packages are removed.
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opkg remove --autoremove luci*
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## Network and device configuration
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- Time configure the network interfaces with `vi`:
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```shell
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root@OpenWrt:~# cat /etc/config/wireless
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config wifi-device radio0
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option type 'mac80211'
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option macaddr '<router_s MAC address here>'
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option hwmode '11g'
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option channel '<channel>'
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option country '<region>'
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option txpower '20'
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# REMOVE THIS LINE TO ENABLE WIFI:
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option disabled '0'
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config wifi-iface
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option device 'radio0'
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option network 'lan'
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option mode 'ap'
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option encryption 'psk2+aes'
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option key '<your key here>'
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option ssid '<your SSID here>'
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root@OpenWrt:~# cat /etc/config/network
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config interface 'loopback'
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option ifname 'lo'
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option proto 'static'
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option ipaddr '127.0.0.1'
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option netmask '255.0.0.0'
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config interface 'lan'
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option ifname 'eth0'
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option type 'bridge'
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option proto 'static'
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option ipaddr '<router_s address>'
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option netmask '<router_s netmask>'
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```
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- If you want to use the router as a switch/repeater, this will disable the
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DHCP server:
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```shell
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/etc/init.d/dnsmasq stop
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/etc/init.d/dnsmasq disable
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```
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# Problems
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There is not enough memory to install anything even after killing several
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processes.
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route add default gateway 192.168.1.1 netmask 0.0.0.0 metric 0
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echo "nameserver 8.8.8.8" > /etc/resolv.conf
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root@OpenWrt:~# opkg install sshfs
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Installing sshfs (2.2-1) to root...
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Downloading http://downloads.openwrt.org/attitude_adjustment/12.09/brcm63xx/generic/packages/sshfs_2.2-1_brcm63xx.ipk.
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Collected errors:
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* gz_open: fork: Cannot allocate memory.
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* opkg_install_pkg: Failed to unpack control files from /tmp/opkg-Ry3bvT/sshfs_2.2-1_brcm63xx.ipk.
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* opkg_install_cmd: Cannot install package sshfs.
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For some reason, WiFi seems less powerful (as in range) than it should be.
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This is quite disappointing.
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# Alternatives
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It would be interesting to patch the original Netgear/SerComm firmware by
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removing the `scfgmgr` file and a line in a shell script that is launched at boot.
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You need a 32 bit GNU/Linux distribution with the appropriate development
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libraries and only then you'll be able to run the software that rebuilds the
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image. Unfortunately there is only a text file describing generic instructions
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so it takes quite some time to track down all the necessary libraries and to have
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a working environment. Maybe another time...
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# Applications using OpenWrt
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I ended up using it for this:
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[openwrt-leds-as-notification](https://github.com/frnmst/openwrt-leds-as-notification)
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