2023-10-06
Tap devices were historically used for VPN clients. Using them for virtual machines is essentially reversing their original purpose - from traffic sinks to traffic sources. In the article I explore the intricacies of tap devices, covering topics like offloads, segmentation, and multi-queue....
2023-07-11
Ping developers clearly put some thought into that. I wondered how far they went. Did they handle clock changes in both directions? Are the bad measurements excluded from the final statistics? How do they test the software?...
2022-11-25
In this blog we'll discuss how we manage Cloudflare IP addresses used to retrieve the data from the Internet, how our egress network design has evolved, how we optimized it for best use of available IP space and introduce our soft-anycast technology...
2022-07-26
In this blog post I'll share my journey deep into the Linux networking stack, trying to understand the memory and window management of the receiving side of a TCP connection...
2022-02-02
Often programmers have assumptions that turn out, to their surprise, to be invalid. From my experience this happens a lot. Every API, technology or system can be abused beyond its limits and break in a miserable way...
2021-11-25
Historically Cloudflare's core competency was operating an HTTP reverse proxy. We've spent significant effort optimizing traditional HTTP/1.1 and HTTP/2 servers running on top of TCP. Recently though, we started operating big scale stateful UDP services....
2021-05-06
Is it ok to have if clauses that will basically never be run? Surely, there must be some performance cost to that......
2020-12-18
Last year we deployed a CSAM image scanning tool. This is so cool! Image processing is always hard, and deploying a real image identification system at a Cloudflare scale is no small achievement! But we hit a problem - the matching algorithm was too slow for our needs....
2020-06-18
My program received a SIGSEGV signal and crashed with "Segmentation Fault" message. Where does the "V" come from? Did I read it wrong? Was there a "Segmentation *V*ault?"? Or did Linux authors make a mistake? Shouldn't the signal be named SIGSEGF? ...
2020-04-06
We were wondering - can we just enable Linux "conntrack"? How does it actually work? I volunteered to help the team understand the dark corners of the Linux's "conntrack" stateful firewall subsystem....
2020-03-02
Last month finally I had an opportunity to use Bloom filters. I became fascinated with the promise of this data structure, but I quickly realized it had some drawbacks. This blog post is the tale of my brief love affair with Bloom filters....
2019-09-20
We noticed something weird - the TCP sockets which we thought should have been closed - were lingering around. We realized we don't really understand when TCP sockets are supposed to time out! We naively thought enabling TCP keepalives would be enough... but it isn't!...
2019-07-10
For some time I’ve wanted to play with coverage-guided fuzzing. I decided to have a go at the Linux Kernel netlink machinery. It's a good target: it's an obscure part of kernel, and it's relatively easy to automatically craft valid messages....
2019-05-18
Recently at I gave a short talk titled "Linux at Cloudflare". The talk ended up being mostly about BPF. It seems, no matter the question - BPF is the answer. Here is a transcript of a slightly adjusted version of that talk....
2019-03-15
Ladies and gentlemen, I would like you to welcome the new shiny RFC8482, which effectively deprecates DNS ANY query type. DNS ANY was a "meta-query" - think about it as a similar thing to the common A, AAAA, MX or SRV query types, but unlike these it wasn't a real query type - it was special....
2019-02-18
Proper TCP socket splicing reduces the load on userspace processes and enables more efficient data forwarding. We realized that Linux Kernel's SOCKMAP infrastructure can be reused for this purpose....
2019-01-04
The Linux AIO is designed for, well, Asynchronous disk IO! Disk files are not the same thing as network sockets! Is it even possible to use the Linux AIO API with network sockets in the first place? The answer turns out to be a strong YES! ...
2018-11-23
I was particularly interested in one of the consequences of how dynamic RAM works. You see, each bit of data is stored by the charge (or lack of it) on a tiny capacitor within the RAM chip. But these capacitors gradually lose their charge over time....
2018-11-12
It's been a while since we last wrote about Layer 3/4 DDoS attacks on this blog. This is a good news - we've been quietly handling the daily onslaught of DDoS attacks. Since our last write-up, a handful of interesting L3/4 attacks have happened. Let's review them....
2018-09-10
Back in 2015 we deployed ECMP routing - Equal Cost Multi Path - within our datacenters. This technology allowed us to spread traffic heading to a single IP address across multiple physical servers....
