Brian's Brain

This blog post references my hands-on feature article 'Homeland Security: Monitoring And Manipulating Remote Residences' in EDN's November 22, 2007 edition. It's one of a series of web addendums to the print writeup.

Back in mid-July, I reported a baffling powerline networking quirk to you. To summarize, if I unplugged and then plugged back in a HomePlug 1.0 Turbo or HomePlug AV adapter, any LAN peripheral(s) 'behind' it would no longer be reachable by any other LAN client connected to my Linksys WRT54GC router via a Wi-Fi tether, unless I employed open firewall holes and addressed the powerline-connected peripheral(s) by its/their WAN address(es), or until I rebooted the router. This problem occurred only over Wi-Fi; CAT5- and other powerline-tethered LAN clients could continue to access the powerline-connected peripheral(s) as normal.

I suspected that some quirk in the switch implementation within the WRT54GC was the root cause of my woes, perhaps coupled with an irregularity in which powerline adapters presented themselves to a switch as compared to traditional CAT5 and Wi-Fi connections. Based on some recent feedback from David Yount, Intellon's Strategic Marketing Engineer, I was on the right track.

This sounds very similar to an issue we run into when we plug/unplug and adapter-swap during testing in our labs. Generally we attribute this to the way the ARP table is (not) updated or (not) refreshed when connected through an Ethernet switch. Not all switches are affected this way, either due to quality or implementation, and often our workaround is to either use a hub or a passive splitter to mitigate the issue during test or troubleshooting....HomePlug AV devices keep a MAC bridge table/history for approximately 15 minutes without traffic. If the powerline network is yanked due to power outage, the table would be wiped as well. This "might" cause confusion with the wireless laptop which could conceivably survive power outage under battery power. The temporary MAC/bridge table is one of the more obvious differences between straight CAT5 and the powerline network.

Speaking of powerline networking, just a few minutes ago (in an unrelated email conversation), Dave alerted me to another HomePlug AV quirk that any of you considering implementing it should be aware of. Apparently, not all HomePlug AV adapter manufacturers employ the same 'HomePlugAV' default encryption password convention (although, according to Intellon, all adapters available through retail channels 'should' employ a consistent default password scheme). What this means is that while HomePlug AV-inclusive gear from different suppliers should plug-and-play inter-operate out-of-box, it won't necessarily do so...you might need to explicitly enter an adapter's Device ID into the network configuration utility in order for its non-standard default password to be overridden and for it to subsequently be 'seen' by the rest of the HomePlug AV topology. Nothing like a nonstandard standard, huh?

p.s...Title reference.