The joys of Linksys WRT 54GL

On Friday there was a thunderstorm. Usually during the storms the surge protection in my radio link antenna's power-over-ethernet power supply trips up and needs to be reset by disconnecting the PSU from the mains for around 10 minutes. This time the usual measure didn't suffice. The lights on the adapter came up, but still there was no connectivity. I reported the problem to the ISP's tech support. The next day the engineer rang up and said that he can connect to the dish at my side.

I connected a laptop directly to the uplink cable, configured the static IP address. Lo and behold, the pings go through. Apparently the uplink Ethernet port on my OpenWRT router got fried.
Luckily, this router does not just have an uplink port and four lan ports, it has a programmable switch and an open firmware (OpenWRT 7.09 "Kamikaze") lets me tap into it.

I looked at /etc/config/network, and found the following lines at the top:

#### VLAN configuration
config switch eth0
option vlan0 "0 1 2 3 5*"
option vlan1 "4 5"


vlan0 is the internal lan, 0-3 are the external lan ports, and 5 is the host port. vlan1 connects the uplink port (4) to the router (5). The asterisk probably means packet tagging. As the router internally has just one physical ethernet port, the internal and external interfaces are virtuals employing the same physical interface. Their packets are distinguished by tags.

So, I changed the config thus:


#### VLAN configuration
config switch eth0
option vlan0 "0 1 2 5*"
option vlan1 "3 4 5"


I rebooted the router and plugged the blue uplink cable into the first LAN port (the numbering of the holes on the router is backwards). Tada! Here's my Internet connection again!