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Unboxing the Last Mile: Introducing Last Mile Insights


10 min read

“The last 20% of the work requires 80% of the effort.” The Pareto Principle applies in many domains — nowhere more so on the Internet, however, than on the Last Mile. Last Mile networks are heterogeneous and independent of each other, but all of them need to be running to allow for everyone to use the Internet. They’re typically the responsibility of Internet Service Providers (ISPs). However, if you’re an organization running a mission-critical service on the Internet, not paying attention to Last Mile networks is in effect handing off responsibility for the uptime and performance of your service over to those ISPs.

Probably not the best idea.

When a customer puts a service on Cloudflare, part of our job is to offer a good experience across the whole Internet. We couldn’t do that without focusing on Last Mile networks. In particular, we’re focused on two things:

  • Cloudflare needs to have strong connectivity to Last Mile ISPs and needs to be as close as possible to every Internet-connected person on the planet.
  • Cloudflare needs good observability tools to know when something goes wrong, and needs to be able to surface that data to you so that you can be informed.

Today, we’re excited to announce Last Mile Insights, to help with this last problem in particular. Last Mile Insights allows customers to see where their end-users are having trouble connecting to their Cloudflare properties. Cloudflare can now show customers the traffic that failed to connect to Cloudflare, where it failed to connect, and why. If you’re an enterprise Cloudflare customer, you can sign up to join the beta in the Cloudflare Dashboard starting today: in the Analytics tab under Edge Reachability.

The Last Mile is historically the most complicated, least understood, and in some ways the most important part of operating a reliable network. We’re here to make it easier.

What is the Last Mile?

The Last Mile is the connection between your home and your ISP. When we talk about how users connect to content on the Internet, we typically do it like this:

 end user to Web Site

This is useful, but in reality, there are lots of things in the path between a user and anything on the Internet. Say that a user is connecting to a resource hosted behind Cloudflare. The path would look like this:

life of a request through Cloudflare on the Internet

Cloudflare is a global Anycast network that takes traffic from the Internet and proxies it to your origin. Because we function as a proxy, we think of the life of a request in two legs: before it reaches Cloudflare (end users to Cloudflare), and after it reaches Cloudflare (Cloudflare to origin). However, in Internet parlance, there are generally three legs: the First Mile tends to represent the path from an origin server to the data that you are requesting. The Middle Mile represents the path from an origin server to any proxies or other network hops. And finally, there is the final hop from the ISP to the user, which is known as the Last Mile.

Issues with the Last Mile are difficult to detect. If users are unable to reach something on the Internet, it is difficult for the resource to report that there was a problem. This is because if a user never reaches the resource, then the resource will never know something is wrong. Multiply that one problem across hundreds of thousands of Last Mile ISPs coming from a diverse set of regions, and it can be really hard for services to keep track of all the possible things that can go wrong on the Internet. The above graphic actually doesn’t really reflect the scope of the problem, so let’s revise it a bit more:

life of a request through Cloudflare showing the true impact of the Last Mile

It’s not an easy problem to keep on top of.

Brand New Last Mile Insights

Cloudflare is launching a closed beta of a brand new Last Mile reporting tool, Last Mile Insights. Last Mile Insights allows for customers to see where their end-users are having trouble connecting to their Cloudflare properties. Cloudflare can now show customers the traffic that failed to connect to Cloudflare, where it failed to connect, and why.

Access to this data is useful to our customers because when things break, knowing what is broken and why — and then communicating with your end users — is vital. During issues, users and employees may create support/helpdesk tickets and social media posts to understand what’s going on. Knowing what is going on, and then communicating effectively about what the problem is and where it’s happening, can give end users confidence that issues are identified and being investigated… even if the issues are occurring on a third party network. Beyond that, understanding the root of the problem can help with mitigations and speed time to resolution.

How do Last Mile Insights work?

Our Last Mile monitoring tools use a combination of signals and machine learning to detect errors and performance regressions on the Last Mile.

Among the signals: Network Error Logging (NEL) is a browser-based reporting system that allows users’ browsers to report connection failures to an endpoint specified by the webpage that failed to load. When a user is able to connect to Cloudflare on a site with NEL enabled, Cloudflare will pass back two headers that indicate to the browser that they should report any network failures to an endpoint specified in the headers. The browser will then operate as usual, and if something happens that prevents the browser from being able to connect to the site, it will log the failure as a report and send it to the endpoint. This all happens in real time; the endpoint receives failure reports instantly after the browser experiences them.

The browser can send failure reports for many reasons: it could send reports because the TLS certificate was incorrect, the ISP or an upstream transit was having issues on the request path, the terminating server was overloaded and dropping requests, or a data center was unreachable. The W3C specification outlines specific buckets that the browser should break reports into and uploads those as reasons the browser could not connect. So the browser is literally telling the reporting endpoint why it was unable to reach the desired site. Here’s an example of a sample report a browser gives to Cloudflare’s endpoint:

The report itself is a JSON blob that contains a lot of things, but the things we care about are when in the request the failure occurred (phase), why the request failed (tcp.timed_out), the ASN the request came over, and the metro area where the request came from. This information allows anyone looking at the reports to see where things are failing and why. Personal Identifiable Information is not captured in NEL reports. For more information, please see our KB article on NEL.

Many services can operate their own reporting endpoints and set their own headers indicating that users who connect to their site should upload these reports to the endpoint they specify. Cloudflare is also an operator of one such endpoint, and we’re excited to open up the data collected by us for customer use and visibility.  Let’s talk about a customer who used Last Mile Insights to help make a bad day on the Internet a little better.

Case Study: Canva

Canva is a Cloudflare customer that provides a design and collaboration platform hosted in the cloud. With more than 60 million users around the world, having constant access to Canva’s platform is critical. Last year, Canva users connecting through Cox Communications in San Diego started to experience connectivity difficulties. Around 50% of Canva’s users connecting via Cox Communications saw disconnects during that time period, and these users weren’t able to access Canva or Cloudflare at all. This wasn’t a Canva or Cloudflare outage, but rather, was caused by Cox routing traffic destined for Canva incorrectly, and causing errors for mutual Cox/Canva customers as a result.

Normally, this scenario would have taken hours to diagnose and even longer to mitigate. Canva would’ve seen a slight drop in traffic, but as the outage wasn’t on Canva’s side, it wouldn’t have flagged any alerts based on traffic drops. Canva engineers, in this case, would be notified by the users which would then be followed by a lengthy investigation to diagnose the problem.

Fortunately, Cloudflare has invested in monitoring systems to proactively identify issues exactly like these. Within minutes of the routing anomaly being introduced on Cox’s network, Canva was made aware of the issue via our monitoring, and a conversation with Cox was started to remediate the issue. Meanwhile, Canva could advise their users on the steps to fix it.

Cloudflare is excited to be offering our internal monitoring solution to our customers so that they can see what we see.

But providing insights into seeing where problems happen on the Last Mile is only part of the solution. In order to truly deliver a reliable, fast network, we also need to be as close to end users as possible.

Getting close to users

Getting close to end users is important for one reason: it minimizes the time spent on the Last Mile. These networks can be unreliable and slow. The best way to improve performance is to spend as little time on them as possible. And the only way to do that is to get close to our users. In order to get close to our users, Cloudflare is constantly expanding our presence into new cities and markets. We’ve just announced expansion into new markets and are adding even more new markets all the time to get as close to every network and every user as we can.

This is because not every network is the same. Some users may be clustered very close together in cities with high bandwidth, in others, this may not be the case. Because user populations are not homogeneous, each ISP operates their network differently to meet the needs of their users. Physical distance from where servers are matters a great deal, because nobody can outrun the speed of light. If you’re farther away from the content you want, it will take longer to reach it. But distance is not the only variable; bandwidth and speed will also vary, because networks are operated differently all over the world. But one thing we do know is that your network performance will also be impacted by how healthy your Last Mile network is.

Healthier networks perform better

A healthy network has no downtime, minimal congestion, and low packet loss.  These things all add latency. If you’re driving somewhere, street closures, traffic, and bad roads will prevent you from going as fast as possible to where you need to be. Healthy networks provide the best possible conditions for you to connect, and Last Mile performance is better because of it.  Consider three networks in the same country: ISP A, ISP B, and ISP C. These ISPs have similar distribution among their users. ISP A is healthy and is directly connected with Cloudflare. ISP B is healthy but is not directly connected to Cloudflare.  ISP C is an unhealthy network. Our data shows that Last Mile latencies for ISP C are significantly slower than Network A or B because the network quality of ISP C is worse.

This box plot shows that the latencies to Cloudflare for ISP C are 360% higher than ISPs A or B.

We want all networks to be like Network A, but that’s not always the case, and it’s something Cloudflare can’t control. The only thing Cloudflare can do to mitigate performance problems like these is to limit how much time you spend on these networks.

Shrinking the Last Mile gives better performance

By placing data centers close to our users, we reduce the amount of time spent on these Last Mile networks, and the latency between end users and Cloudflare goes down. A great example of this is how bringing up new locations in Africa affected the latency for the Internet-connected population there.  Blue shows the latency before these locations were added, and red shows after:

Our efforts globally have brought 95% of the Internet-connected population within 50ms of us:

You will also notice that 80% of the Internet is within 30ms of us. The tail for Last Mile latencies is very long, and every data center we add helps bring that tail closer to great performance. As we expand into more locations and countries, more of the Internet will be even better connected.

But even when the Last Mile is shrunken down by our infrastructure expansions, networks can still have issues that are difficult to detect. Existing logging and monitoring solutions don’t provide a good way to see what the problem is. Cloudflare has built a sophisticated set of tools to identify issues with Last Mile networks outside our control, and help reduce time to resolution for this purpose, and it has already found problems on the Last Mile for our customers.

Cloudflare has unique performance and insight into Last Mile networking

Running an application on the Internet requires customers to look at the whole Internet. Many cloud services optimize latency starting at the first mile and work their way out, because it’s easier to optimize for things they can control. Because the Last Mile is controlled by hundreds or thousands of ISPs, it is difficult to influence how the Last Mile behaves.

Cloudflare is focused on closing performance gaps everywhere, including close to your users and employees. Last mile performance and reliability is critically important to delivering content, keeping employees productive, and all the other things the world depends on the Internet to do. If a Last Mile provider is having a problem, then users connecting to the Internet through them will have a bad day.

Cloudflare’s efforts to provide better Last Mile performance and visibility allow customers to rely on Cloudflare to optimize the Last Mile, making it one less thing they have to think about. Through Last Mile Insights and network expansion efforts — available today in the Cloudflare Dashboard,  in the Analytics tab under Edge Reachability — we want to provide you the ability to see what’s really happening on the Internet while knowing that Cloudflare is working on giving your users the best possible Internet experience.

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Vasilis Giotsas|@GVasilis

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