DD-WRT on Linksys

I have been using a Linksys WRT3200ACM (with DD-WRT installed) for a while now and I decided to make a better use of such a high-end WiFi router. These are some notes that worth to write down:

DD-WRT as a NAS

Such router goes with 512MB memory and 256MB flash in two partition. So theoretically each flash can be as big as 128MB. The DD-WRT in such size goes with a newer kernel and a better suite of software. Mine is running 4.9 kernel. Even the kernel has exfat module, it does not seem to work. The USB storage in exfat is recognized but cannot be mounted. If we try to mount it in command line, the terminal hangs (only the system blocks that command, but the router does not, you cann launch a new SSH session into it). Partitions formatted in ext4 works perfectly however.

I make use of the external disk to install Entware, which is like an apt-get in the DD-WRT environment, but with limited number of packages available. Entware is mandatory to install to /opt. So I mounted the partition there. As the Linksys is running ARMv7, this is the command to install:

cd /opt
wget http://bin.entware.net/armv7sf-k3.2/installer/generic.sh
sh generic.sh
opkg update
opkg upgrade

it is suggested to add these to the DD-WRT start-up script:

sleep 10; /opt/etc/init.d/rc.unslung start

and this to the shutdown script:

/opt/etc/init.d/rc.unslung stop

but what these seems to do is only to call the init scripts in case of any installed under Entware environment. Hence optional if no daemon is installed.

For the USB disk connected to the router, we can share it using Samba (under service → NAS), as public share (no authenatication required) or username/password share.

PXE boot

In a full featured system, there are way more options available. It is not the case under DD-WRT. The DHCP server in DD-WRT (DNSmasq) can send responses with boot options. While DNSmasq also goes with TFTP server, the version in DD-WRT is a stripped down one, so you need another TFTP daemon from from Entware. This is to install tftpd-hpa and launch it with xinetd:

opkg install xinetd
opkg install tftpd-hpa
mkdir /opt/tftproot
mkdir /opt/tftproot/pxelinux.cfg

then make this into /opt/etc/xinetd.d/tftp so that xinetd can launch the TFTP server:

service tftp
{
    flags            = REUSE
    socket_type      = dgram
    protocol         = udp
    instances        = 30
    wait             = yes
    user             = root
    server           = /opt/sbin/tftpd-hpa
    server_args      = -4 -B 1468 -s /opt/tftproot
    cps              = 100 2
    log_on_success   = HOST PID
    log_on_failure   = HOST
    disable          = no
}

and this into /opt/tftproot/pxelinux.cfg/default as the boot menu:

DEFAULT menu.c32

PROMPT 1
TIMEOUT 300
ONTIMEOUT Debian x64 Diskless

LABEL reboot
        MENU LABEL reboot computer
        COM32 reboot.c32

LABEL local
        MENU LABEL boot local drive
        LOCALBOOT 0

LABEL Debian x64 Diskless
        MENU LABEL Debian x64
        KERNEL vmlinuz
        APPEND vga=858 rw ip=dhcp initrd=initrd.img root=/dev/nfs nfsroot=192.168.1.1:/debianroot

Optionally, we can also install vim with Entware. To help editing files in console. Then we need to copy the files pxelinux.0, ldlinux.c32, menu.c32 into the TFTP root directory (/opt/tftproot/), and prepare the installed OS at the NFS mount location.

After all is done, add the following to the “Additional DNSMasq Options” in the DD-WRT webui, under Services → Services:

dhcp-boot=pxelinux.0,gateway,192.168.1.1

Then the client who’s booting with PXE will work. (Note: Because we add the DHCP option to DNSMasq, we have to make sure we are using it as DHCP server. This is configured at Setup → Network Setup → DHCP → Use DNSMasq for DHCP)

SSH on DD-WRT

The SSH server (as well as client) are dropbear, but only compiled with RSA (for size concern?). Therefore, we can only assign a RSA key for authentication if you prefer not to use password-based.