While many of us were discussing Comcast’s partial blocking of BitTorrent Traffic, and debating its implications for the net neutrality debate, a more clear-cut neutrality violation was apparently taking place on Verizon’s network – a redirection of Verizon customers’ failed DNS lookups, to drive traffic to Verizon’s own search engine.

Here’s the background. Suppose you’re browsing the web and you mistype an address – say you type “fredom-to-tinker”. Your browser will try to use DNS, the system that maps textual machine names to numeric IP addresses, to translate the name you typed into an address it can actually connect to across the Net. DNS will return an error, saying that the requested name doesn’t exist. Your browser (if it’s a recent version of IE or Firefox) will respond by doing a search for the text you typed, using your default search engine.

What Verizon did is to change how DNS works (for their residential subscribers) so that when a customer’s computer looks up a DNS name that doesn’t exist, rather than returning the name-doesn’t-exist error DNS says that the (non-existent) name maps to Verizon’s search site. This causes the browser to go to the Verizon search site, which shows the user search results (and ads) related to what they typed.

(This is the same trick used by VeriSign’s ill-fated SiteFinder service a few years ago.)

This is a clear violation of net neutrality: Verizon is interfering with the behavior of the DNS protocol, in order to drive traffic to its own search site. And unlike the Comcast scenario which might possibly have been justifiable as legitimate network management, in this case Verizon cannot claim to be helping its network run more smoothly.

Verizon’s actions have two effects. The obvious effect is to drive traffic from the search engines users chose to Verizon’s own search engine. That harms users (by overriding their choices) and harms browser vendors (by degrading their users’ experiences).

The less obvious effect is to break some other applications. DNS lookups that have nothing to do with browsing will still be redirected, because the DNS infrastructure has no way of knowing which requests relate to browsing and which don’t. So if some other application does a DNS lookup and the result should be a not-found error, Verizon will cause the result to point to a Verizon server instead. If a non-browser program expects to see not-found errors sometimes and has a strategy for dealing with them, it won’t be able to carry out that strategy because it won’t see the errors it should be seeing. This will even cause browsers to misbehave in some circumstances.

The effects of Verizon’s neutrality violation can be summarized simply: they interfer with a standard technical protocol; they cause harm on the whole, in part by breaking unrelated services; and they do this in order to override consumer choice by shifting traffic from consumer-chosen services to Verizon’s own services. This is pretty much the definition of a net neutrality violation.

This example contradicts at least two of the standard arguments against net neutrality regulation. First, it shows that violations do happen, and they do cause harm. Second, it shows that at least sometimes it’s easy to tell a harmful violation apart from legitimate network management.

But it doesn’t defeat all of the arguments against net neutrality regulation. Even though violations do occur, and do cause harm, it might turn out that the regulatory cure is worse than the disease.

The revelation that Comcast is degrading BitTorrent traffic has spawned many blog posts on how the Comcast incident bolsters the blogger’s position on net neutrality – whatever that position happens to be. Here is my contribution to the genre. Mine is different from all the others because … um … well … because my position on net neutrality is correct, that’s why.

Let’s start by looking at Comcast’s incentives. Besides being an ISP, Comcast is in the cable TV business. BitTorrent is an efficient way to deliver video content to large numbers of consumers – which makes BitTorrent a natural competitor to cable TV. BitTorrent isn’t a major rival yet, but it might plausibly develop into one. Which means that Comcast has an incentive to degrade BitTorrent’s performance and reliability, even when BitTorrent isn’t in any way straining Comcast’s network.

So why is Comcast degrading BitTorrent? Comcast won’t say. They won’t even admit what they’re doing, let alone offer a rationale for it, so we’re left to speculate. The technical details of Comcast’s blocking are only partially understood, but what we do know seems hard to square with claims that Comcast is using the most effective means to optimize some resource in their network.

Now pretend that you’re the net neutrality czar, with authority to punish ISPs for harmful interference with neutrality, and you have to decide whether to punish Comcast. You’re suspicious of Comcast, because you can see their incentive to bolster their cable-TV monopoly power, and because their actions don’t look like a good match for the legitimate network management goals that they claim motivate their behavior. But networks are complicated, and there are many things you don’t know about what’s happening inside Comcast’s network, so you can’t be sure they’re just trying to undermine BitTorrent. And of course it’s possible that they have mixed motives, needing to manage their network but choosing a method that had the extra bonus feature of hurting BitTorrent. You can ask them to justify their actions, but you can expect to get a lawyerly, self-serving answer, and to expend great effort separating truth from spin in that answer.

Are you confident that you, as net neutrality czar, would make the right decision? Are you confident that your successor as net neutrality czar, who would be chosen by the usual political process, would also make the right decision?

Even without a regulatory czar, wheels are turning to punish Comcast for what they’ve done. Customers are unhappy and are putting pressure on Comcast. If they deceived their customers, they’ll face lawsuits. We don’t know yet how things will come out, but it seems likely Comcast will regret their actions, and especially their lack of transparency.

All of which – surprise surprise – confirms my position on net neutrality: there is a risk of harmful behavior by ISPs, but writing and enforcing neutrality regulation is harder than it looks, and non-regulatory forces may constrain ISPs enough.