Pre and Post Checks with Ansible

Pre and Post Checks with Ansible

This post is part of an ongoing series - see all the posts below.

Ansible Course

In the previous part, we wrote two checks for our OSPF network. One makes sure every router has all of its OSPF neighbours, and the other makes sure every router can reach every other router's loopback. They're useful on their own, but they're even more useful when you run them around a change.

The idea is that before making a change, you check that the network is healthy. If it isn't, you stop, since there's no point making a change on a network that's already broken. It also means that if something goes wrong later, you know it wasn't already broken before you started. Then, after the change, you run the same checks again to make sure everything is still healthy.

Most of us already do this manually. Before a change, we log in and save the output of a few show commands, and afterwards, we run them again and compare. In this part, we'll let Ansible do it for us, by reusing the playbooks we've already written, rather than copying them into every change playbook.

We're continuing with the same lab and Continue reading

4 real? Tracking exploitation and patching of eMudhra’s weak keys

On October 19, 2026, we learned about eMudhra’s eight shockingly weak keys: where eMudhra was trusted to pick a 115-digit number for their virtual combination lock protecting the Internet, they picked the number 4. Not even four digits, just the number 4. The other seven keys were similarly weak: 56, 66, 115, 155, 156, 230 and 237.

The next day, we wrote a blog post on the immediate action we took to mitigate this leak, and what customers needed to do on their end to stay secure. Now, we are sharing a more in-depth follow up on the evidence we’ve seen of exploitation, and the progress seen on visitors patching their systems.

Let's start with the scale of the problem. A certificate authority (CA) with weak keys this serious is unprecedented, and the potential consequences are significant. While there have been plenty of compromised certification authorities in the past (such as DigiNotar, TÜRKTRUST, and TrustWave), access to their keys has always been contained to a degree; these incidents gave a limited set of attackers or organizations the ability to issue fraudulent certificates. The eMudhra incident is fundamentally different; the affected intermediate private keys could be recovered almost Continue reading

Cloudflare services for private origins is now generally available

Today, Cloudflare services for private origins is generally available. Point a proxied DNS record at a private IP, and Cloudflare reaches the origin over your existing Cloudflare One connection. Your origin stays private, while web application firewall (WAF), caching, bot management, and Workers work just as they do for public origins.

In June, we launched this capability in closed beta to address a problem we kept hearing from customers: Their internal APIs, AI agent backends, MCP servers, and operational tools weren’t built to face the Internet, but those services still need to accept requests from partners, customers, or agents over the Internet. Before the beta, putting Cloudflare in front of these services meant exposing a public IP, opening a firewall port, or running cloudflared alongside the origin.

Those requirements often left private applications without the same protections and controls they used for public applications, including WAF, bot management, rate limiting, caching, traffic acceleration, rewrites, and Workers.

What is generally available today

During the closed beta, eligible customers requested access through their account team. Today, we’re opening access beyond that beta group.

Point a proxied A or AAAA record at a private IP, and Cloudflare’s application services work Continue reading

When Novel Becomes Normal

Imagine your product strategy team gets stuck on a positioning problem. Somebody opens an AI chat window and asks for an unconventional angle. The model comes back with a concept nobody in the room has thought about in years. Maybe it’s the Lindy effect or Chesterton’s fence or something borrowed from evolutionary biology. The room loves it. It feels fresh and a little clever. Three months later a competitor walks onto a keynote stage with the same framing. How did that happen? Did someone leak the deck?

You’ve probably felt a smaller version of this. You learn a new word and it shows up in three articles that same week. The linguist Arnold Zwicky named this on Language Log in 2005. He called it the frequency illusion, though you may know it by its folk name, the Baader-Meinhof phenomenon. Once you notice something, you think it’s everywhere. Most of the time it isn’t. Your attention changed. The world didn’t. When the coincidences really start piling up, some people reach for something grander. Great minds think alike. Ideas are in the air. Maybe there’s a universal consciousness out there that we’re all dipping into. Or maybe it’s as bland as Continue reading

Cloudflare DDoS Threat Report 2026 Q3: More swarms, fewer giants

Welcome to the 26th edition of Cloudflare's DDoS Threat Report. This edition covers the third quarter of 2026 — July, August, and September — and returns the series to its quarterly cadence following the combined H1 2026 volume. The analysis is produced by Cloudforce One, Cloudflare's Threat Intelligence organization, providing a comprehensive analysis of the evolving threat landscape of Distributed Denial of Service (DDoS) attacks based on data from the Cloudflare network.

Key insights

  1. Short-burst, low-bandwidth attacks lasting under 10 minutes and 1 Gbps surged by 208%. Conversely, hyper-volumetric attacks exceeding 1 Tbps plummeted by nearly 69% from Q2, possibly a reflection of law enforcement actions against four major Internet of Things (IoT) botnets earlier in the year. However, variants continue to emerge, proving that IoT botnets remain a durable, high-volume threat to network infrastructure.
  2. Threat actors dramatically shifted their reflection and amplification tactics, abruptly abandoning CLDAP floods, which collapsed by 99.5% quarter-over-quarter. Instead, attackers pivoted heavily toward other connectionless protocols, driving a 215% surge in DNS amplification and a 122% increase in general UDP floods.
  3. Attack targets broadened significantly across both industries and geographies, with the United States reclaiming the most-attacked position from China. Canada and Israel Continue reading

Fabric Topologies for GPU Clusters

In part five of a series on AI data center networking, various interconnected networks are discussed, highlighting the differences between traditional and AI clusters. Key topics include back-end and front-end networks, the folded-Clos topology, adaptive routing, and the significance of switch design in addressing network congestion. Dragonfly topology is also mentioned for hyperscale systems.

The post Fabric Topologies for GPU Clusters appeared first on /overlaid.

Booth Demo

Quickly engaging an audience is a challenge at a trade show - all Ethernet switches look pretty much the same and they don't do much other than blink LEDs. Real-time sFlow telemetry is a core feature of switches that can be used to create intriguing animated dashboards that draw customers into the booth by demonstrating how the switch addresses their needs.

The example above uses the open source sFlow-RT booth-demo application to demonstrate a 400G data center switch carrying RoCEv2 test traffic. The demo shows a series of RDMA write operations in the Traffic Trend chart. The Switch Port Traffic Flows diagram shows the paths traffic takes as it flows through the switch. In this example, a NCCL ring topology results traffic flowing from port to port as it goes around the logical ring of GPUs.

The quickest way to set up the demo is to run the a pre-built sflow/booth-demo image on a laptop connected to the booth display screen. The Traffic Trend chart is easily customizable to show different flow attributes that are relevant to the demo and the title can be changed to include branding and messaging. If more extensive customization is required, clone the GitHub project Continue reading

Validating Your Network with Ansible Assert

Validating Your Network with Ansible Assert

This post is part of an ongoing series - see all the posts below.

Ansible Course

In the previous part, we built an OSPF network from scratch using Ansible, and then logged in to the routers to check that everything was working. We looked at the OSPF neighbors, checked the routing table, and ran a few pings. That's fine for six routers. But imagine doing it for fifty, before and after every change, at 2 AM during a maintenance window. By router number twelve, you're not really reading the output anymore, you're just looking for the word FULL and hoping for the best.

In this part, we'll let Ansible do the checking for us. We'll write a few simple tests that check whether every router has the right number of OSPF neighbors, and whether every router can reach every other router. If something is wrong, the playbook fails and tells us exactly where the problem is. We'll also break the network on purpose, so we can see what happens when a check fails.

We're continuing with the same lab and project from the previous part, so if you haven't read it yet, I recommend starting there.

What Is assert?

Continue reading

Fixing SCHED_IDLE for real

I’ve wondered for years why SCHED_IDLE tasks are allowed to preempt other tasks. Nobody seems to know, and I’ve not had the time to dig in and understand the Linux kernel scheduler better. But now I finally have my answer.

The problem

I want to be able to run a CPU-heavy task in the background, without it stealing any CPU, any at all, from other processes.

If you read various documentation, you’d be forgiven if this is as simple as schedtool -D -e ./my-background-thing.

SCHED_FIFO can be used only with static priorities higher than 0,
which means that when a SCHED_FIFO thread becomes runnable, it
will always immediately preempt any currently running SCHED_OTHER,
SCHED_BATCH, or SCHED_IDLE thread.

(and similar statements, e.g. from sched.7)

But if you try that, you’ll find that it’ll actually preempt other processes, taking little but nonzero CPU. There’s a test program, if you want to try it out.

I literally want it to take zero CPU. And not just against SCHED_FIFO/RR, but everything.

The existing settings

There appear to be two places that minmax guarantees can show up.

Settings with default values:

$ sudo sysctl -a | grep sched_rt_
kernel. Continue reading

Global Infrastructure at NANOG 98

The most recent North American Network Operators Group (NANOG) meeting was held in mid-October 2026 in Miami. The opening keynote presentation was by Telegeography's Paul Brodsky on the topic of global Internet Infrastructure. His presentation highlighted a structural shift in global Internet infrastructure, with visible concentration of investment and control in a small number of hyperscalers.

Introducing the Cloudflare PHP Capture the Flag challenge

Last week was one for the Internet security history books. First, eight eMudhra intermediate certificates were compromised, creating the possibility of forged certificates that could be used to impersonate servers. Then came php2shell: serious vulnerabilities in PHP, the runtime behind a large portion of the Web.

Cloudflare worked around the clock as these events unfolded to protect our customers and help protect the Internet. We shipped client updates and multiple mitigations, updated our web application firewall (WAF) with new rules to block attackers from exploiting the PHP vulnerabilities, and introduced a new feature called full transaction detection.

As always in situations like this, these new capabilities were made available on all plans, including Free.

Put our WAF to the test

Protecting systems from vulnerabilities like these is always an ongoing process, not a one-time event. The widespread adoption of AI allows attackers to discover new vectors with unprecedented speed and efficiency, so collecting real-world data to test our assumptions and strengthen defenses is essential.

That’s why today we're launching the Cloudflare PHP Capture the Flag challenge, run through our Bug Bounty program. We've put a deliberately vulnerable PHP installation behind our WAF, and we're inviting security researchers Continue reading

What took the Internet offline in Q3 2026

The Internet can feel invisible when everything is working normally. But when connectivity breaks, the many systems it depends upon become evident in an instant. Because Cloudflare’s global network handles more than 20% of the web’s traffic, it offers a unique perspective of how Internet traffic is behaving. When failures in infrastructure, power, policy, or security disrupt access to the Internet, Cloudflare Radar can observe the impact by monitoring traffic to our customers. Each quarter, we review the disruptions detected and annotated on Radar, highlighting what happened, where it happened, and the broader conditions that shaped each event.

In this post, we examine the major categories of Internet disruptions observed during the third quarter of 2026, including government-directed shutdowns, power outages and natural disasters.

Disruptions at a glance

Between July and September, Internet disruptions were largely driven by failures in the systems the Internet depends on. Power grids failed in Cuba, Honduras, Guam, Ukraine, and several other countries. Natural disasters damaged electricity and telecommunications infrastructure from Nepal to Colombia. Government-directed shutdowns remained the most frequent source of disruption, driven largely by exam-related shutdowns in Iraq, while renewed conflict in Ethiopia’s Tigray region showed how quickly connectivity can become part of Continue reading

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