New rules that affect open source firmware on Wi-Fi routers will be implemented on June 2, but not all network hardware will prevent the loading of third-party software.

Linksys has been collaborating with chipmaker Marvell and the makers of OpenWrt to make sure its latest WRT routers can comply with the new rules without blocking open source firmware, company officials told Ars.

Linksys’s effort stands in contrast with TP-Link, which said it would entirely prevent loading of open source firmware on its routers to satisfy the new Federal Communications Commission requirements.

Blocking third-party firmware is the easiest way to comply with the FCC rules, which aim to limit interference with other devices by preventing user modifications that cause radios to operate outside their licensed RF (radio frequency) parameters.

The FCC wrote its rules in response to interference with FAA Doppler weather radar systems. Routers using certain portions of the 5GHz band were already required to use dynamic frequency selection (DFS) in order to detect nearby radar systems and avoid operating on the same channel. But it’s possible for users to disable dynamic frequency selection—the FCC has called this a “major cause of harmful interference.” Most cases of interference have been caused either by disabling DFS or “devices that have been modified to operate in frequency bands in which they are not certified to operate,” the FCC says.

“Our responsibility to the open source community”

Any 5GHz routers sold on or after June 2 must include security measures that prevent these types of changes. But router makers can still allow loading of open source firmware as long as they also deploy controls that prevent devices from operating outside their allowed frequencies, types of modulation, power levels, and so on.

This takes more work than simply locking out third-party firmware entirely, but Linksys, a division of Belkin, made the extra effort. On and after June 2, newly sold Linksys WRT routers will store RF parameter data in a separate memory location in order to secure it from the firmware, the company says. That will allow users to keep loading open source firmware the same way they do now.

Other Linksys routers, such as Max-Stream devices, will block open source firmware. But continuing support on the WRT line is a natural move for Linksys, given that the OpenWrt and DD-WRT third-party firmware was originally built for the company’s WRT54G routers more than a decade ago.

“They're named WRT… it's almost our responsibility to the open source community,” Linksys router product manager Vince La Duca told Ars.

WRT stands for “Wireless RouTer,” and Linksys has stuck with its naming conventions and support for open source for many years. The “WRT54GL” released in 2005 offered speeds of up to 54Mbps. The “L” stood for Linux.

Linksys resurrected the classic blue and black design of the WRT in 2014 with the new WRT1900AC. The numbers and letters indicated support for up to 1900Mbps and the 802.11ac Wi-Fi standard. That router as well as the newer WRT1900ACS and WRT1200AC will continue to support open source firmware after the new rules take effect, La Duca said.

"The hardware design of the WRT platform allows us to isolate the RF parameter data and secure it outside of the host firmware separately," Linksys said in a written statement given to Ars.

La Duca declined to get more specific about Linksys's exact method. Even though this is about enabling open source, Linksys’s method is proprietary and provides a competitive advantage over other router makers that aren’t supporting open source, La Duca said.

Using open source isn’t about breaking the rules

While Linksys’s support of open source is partly a marketing strategy, La Duca understands why customers want to use OpenWrt and similar software.

“The real benefit of open source is not breaking the rules and doing something with malicious intent, the value of open source is being able to customize your router, to be able to do privacy browsing through Tor, being able to build an OpenVPN client, being able to strip down the firmware to do super lean, low-latency gaming,” La Duca said. “It's not about ‘I'm going to go get OpenWrt to go and piss off the FCC.' It's about what you can do in expanding the capabilities of what we ship with.”

But that doesn’t extend across all Linksys routers. For Max-Stream devices and other routers that lack WRT branding, “open source is not a value proposition that we are promoting,” La Duca said. For those non-WRT platforms, Linksys is not working with chip providers to enable open source support.

"All Linksys legacy and Max-Stream routers will have the full host firmware locked down," the Linksys statement said. The company noted that these routers were never marketed to open source users as the WRT routers are.

Whether open or closed, Linksys said all of its dual- and tri-band routers will comply with the new FCC rules "that require our routers and software to be secured to prevent changing the power output or unauthorized channel selection of the router on the 5Ghz band." (There are also similar new requirements implemented by the European Telecommunications Standards Institute, Linksys said.)

“No one else was prepared for this”

Imre Kaloz, a key OpenWrt developer, told Ars that he isn't aware of any other vendors making a similar effort to support open source. Kaloz has tried to get other hardware makers interested, but he said his attempts have so far only earned him some marketing e-mails.

Still, Kaloz holds out hope that other vendors will see the work that Linksys has done and try to copy it. “It's not that complicated, it's simply that no one else was prepared for this,” Kaloz said.

Most of the necessary changes happened on the hardware side, Kaloz said. But OpenWrt developers also worked closely with Marvell to update the open source wireless driver so that OpenWrt can continue to work, he said.

Default OpenWrt functionality will remain unchanged on Linksys WRT routers, Kaloz said. It’s open source and can thus be modified, but by default OpenWrt doesn’t let users do anything that would violate FCC rules, he said.

DD-WRT, which is based on OpenWrt, is capable of disabling DFS.

Although Linksys has proven that open source firmware can still be used under the new FCC rules, it’s clear that options for open source users will be more limited than they are today. Kaloz wishes the FCC had taken a different approach, one focused on punishing people who cause interference without preventing legitimate uses of network hardware.

The decisions, he said, "have been made by lawyers who had not too much technical knowledge."