This page contains information about getting the Adhoc On-demand
Distance Vector (AODV) Routing protocol on the Linksys WRT54G
wireless broadband router. AODV is a reactive routing protocol for
wireless adhoc networks. The WRT54G
is a wireless broadband router solution that runs Linux and supports
the IEEE 802.11 adhoc mode. It is available for under $70 at most
retail websites. Moreover, its easy to turn the
WRT54G into a wireless mesh box. This enables one to create an
economical wireless mesh network
in quick time. Given below are a set of instructions on transforming a
stock WRT54G device into a wireless mesh box that uses AODV for routing
within the mesh.
I recommend using the openwrt
firmware
for running AODV. The openwrt project has created a simple, no-frills
Linux distribution for the WRT54G. Because the openwrt firmware offers
only the bare minimum to run Linux on the WRT54G, you can customize the
base installation however you require. Offcourse, openwrt is not the
only distribution to support the WRT54G. Other distributions are
available such as ones from Sveasoft.
Sveasoft's distribution is kinda neat because it comes bundled with a
bunch of additional software. However, their firmware offers more than
I need. I wanted something light-weight and easily manageable and
therefore I choose the openwrt firmware. From what I read online,
people have successfully executed AODV using the Sveasoft firmware. So,
if you need to use the Sveasoft firmware, please search for it.
As for the choice of the openwrt firmware, I used their stock firmware
available here.
Since openwrt updates their distribution on a daily basis, the version
you choose will be different from the version I use. If you want to in
stead proceed with the firmware I use, you can download my version from
here. In any case, I would highly
recommend that you compile the firmware from the sources because you
will need the mips cross-compiler, available as part of the source
package, to compile AODV for the WRT54G. Check the openwrt user-guide for
instructions on compiling the firmware from the source.
After successfully compiling the firmware, you need to install your
choice of the openwrt firmware on your router. The best way to do this
is to use the html based management interface offered by the
factory-default Linksys firmware. Click on the "management" tab on the
main html page and then click on the "firmware upgrade" link to install
the openwrt firmware. Comprehensive instructions on howto install the
openwrt firmware are available on this openwrt web-page. It is very
important that you turn on the "boot_wait" nvram setting on the router
before the upgrade or else you may end up with bricking your device
due to a faulty firmware. Here is an excellent page on debricking
your WRT54G.
Step 2: Device
Configuration
Once you have installed the openwrt firmware on device, the next step
is to configure the device to operate in adhoc mode. Before the device
configuration, might I also recommend that you install the dropbear ssh
package on the device. Here is a handy page with
installation instructions and some getting started tips.
Now, lets get straight to the device configuration. First, you need to
telnet/SSH into the box. Next, you have the
choice of using the br0 interface or disabling it. This interface
bridges the lan ports and wireless interface as a virtual br0 inteface,
which means that both the lan and the wireless share the same IP range.
This may be required when you use the WRT54G as an access point.
However, when operating the device in adhoc mode, this feature is
probably not required. I have disabled the br0 interface on my device,
and you can do this by executing the following commands:
nvram set
lan_ifname=vlan0 nvram unset
lan_ifnames nvram set
wifi_ifname=eth1
nvram commit
The first command,
above, sets the lan_ifname
NVRAM setting to the lan interface vlan0 instead of br0.
It then sets the wireless interface to interface eth1.To configure the wireless
interface to operate in adhoc mode, execute the following commands: nvram
set wifi_proto=static nvram set
wifi_ipaddr=<adhoc IP address> nvram set
wifi_netmask=<netmask> nvram set
wl0_mode=sta nvram set
wl0_infra=0 nvram set
wl0_ssid=<adhoc essid> nvram commit
The above commands configure the wireless interface on the WRT54G to
operate in adhoc mode. At this point, you should reboot the router and
check if you can ping another device operating in
adhoc mode on the same essid. If all is well, proceed to the next step.
If you are not able to ping the other device, something is obviously
wrong, and you need to troubleshoot the problem. The best way to check
if your interface is correctly configured is to run iwconfig eth1 on the router as
a first step. A
typical iwconfig command output should look similar to this:
Of interest in your command output are the fields marked in red
above. The values for the four fields on the two devices should
be the same. If they are not, check to make sure that you configured
both devices correctly. If the values for the four fields are the same,
the next thing to do is to ensure that you have no firewalls rules that
are blocking ICMP packets. Another option you can try out is to run a
packet sniffer
to see whats being exchanged between the two devices on the wireless
channel and then to proceed from there.
Step 3: AODV Compilation
I use the NIST
implementation for most of my work, which is why I describe the
procedure to compile that package for the WRT54G. I recently modified this AODV implementation and the protocol itself to support a reliability based metric. The enhanced protocol is called AODV-ST. More information about AODV-ST can be found here. I would recommend that you use AODV-ST instead of AODV for two reasons: (1) AODV-ST extends AODV through the support of routing metrics, and (2) the AODV-ST implementation addresses some bugs/issues with the NIST AODV implementation. If you are looking for AODV only, you can use either the NIST AODV implementation or one of the others indexed
here. If you are using AODV-ST, please note the caveat specific to the WRT54G on the download page for AODV-ST.
Assuming that you are using either the NIST or the AODV-ST implementation, you will need to modify the Makefile in
the package to contain the correct path information of the mips
cross-compiler. Given below is a diff of the modified Makefile and the
original Makefile.
Next, you can compile the aodv module by running make. Thats all there is as far
as compiling aodv is concerned.
Step 4: AODV Execution
Before you can run AODV, you need to copy AODV onto the linksys device.
Use either scp or wget to copy the kernel_aodv.o (or aodv-st.o) file to the
device. To execute AODV, simply run the following command:
insmod
the_aodv_module use_dev=eth1
Thats it! Everything should be hunky-dory now! Enjoy your new
AODV mesh box!
