The Calypso project leverages traceroute data to provide detailed maps of the submarine cables.
Julia Evans has contributed new examples to the tcpdump manpage.
Flavio Luciani shares traffic graphs from an Indonesian IXP showing how Internet traffic changes during Ramadan.
In a series of posts on Mastodon, Kenneth Finnegan describes in detail what’s inside a 100 Gbps LR4 optic. Interesting read if you’d like to understand what’s inside these « connectors ».
Geoff Huston provides a nice explanation on how time is managed on the Internet.
A nice visualisation based on DNS MX records shows where email of 2,100 Swiss municipalities are hosted.
In a short article published in IEEE Spectrum, Malik Tatipamula and Vint Cerf describe the last 40 Years of Wireless Evolution in cellular networks and the evolution from 1G to the forthcoming 6G.
The IPv6 over nothing IETF draft proposes to use IPv6 without an underlying datalink layer.
TLS Encrypted Client Hello is now officially published as RFC9849. Samuel Henrique explains in a short blog post how to use ECH with curl on Debian.
In a short blog post, Mark Nottingham explains how he used Notebook LLM to analyze the progress of IETF working groups.
Another demonstration of the importance of network connectivity. In Nordic countries, a large fractions of the payments in shops are done online. To cope with the risks of massive network disruptions, a new law enables offline payments in case of major network disruptions.
A set of Claude skills to explore the 3GPP specifications, from 2G to 6G.
An interesting blog post showing how a cheap NTP server evolved over time to obtain 26 nanosecond clock accuracy.
Linus Torvalds has started to remove old networking code from the Linux kernel. This removal affects protocols such as AX.25 (amateur radio), ATM, and old Ethernet drivers.
Reflections on the implementation of the Carrier Pigeon Internet Protocol, RFC1149, 25 years later
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>Bruce Davie discusses the potential impact of improved shortest path computation algorithms on link state routing protocols such as OSPF and IS-IS.
Ivan Pepeljnak provides interesting information about the performance of routers thirty years ago and how they shaped some of the design of MPLS.
Since the early days of the Internet, telnet has been a very popular method to access remote servers. It has been slowly replaced by ssh since the late 1990s. Recently, a severe flaw has been identified in one of the most popular implementations of telnet that is deployed on a wide range of embedded devices. A recent study shows that multiple ISPs have started to block TCP on port 23 to prevent exploitation of this vulnerability.
An interesting NANOG presentation describes the BGP architecture of the Netflix network.
The BGP clock is an interesting experiment that allows detection of BGP zombies on the Internet. A BGP zombie is an IP prefix that has been withdrawn but whose route is still present in some routers.
Geoff Huston provides his annual review of the evolution of the global BGP routing tables.
A free IP geolocation database is available from https://ip66.dev/.
Arelion, aka AS1299, one of the international Tier-1 ISPs, provides an interesting graph on the evolution of the traffic that it carries.
Mike Nottingham wrote an interesting opinion explaining why the Internet is and should remain an open system.
Internet exchange Points (IXP) are a key component of the Internet as they allow ISPs to peer at different locations. Tommaso Caiazzi shows how to build a digital twin to reproduce such an IXP using Kathara.
The BBR congestion control algorithm is replacing the CUBIC algorithm in some TCP implementations. A recent survey (36 pages!) summarizes the literature on this congestion control scheme and provides some measurement results.
Mingwei Zhang and Bryton Herdes provide a nice description of the Autonomous System Provide Authorization (ASPA) that extends the RPKI to secure interdomain routing.
Some git repositories are being overloaded by companies that create thousands of git pulls per day due to misconfiguration or bad practices.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>Ookla reveals interesting data about the uplink capacity in 5G networks.
Job Snijder published his yearly summary of the evolution of the RPKI on the NANOG mailing list.
Nice video showing how passkeys work to authenticate users on web sites.
Luc de Brandere posted on LinkedIn a really nice drawing by Alix Garin to celebrate the 25th birthday of Wikipedia which continues to operate outside today’s surveillance economy.
A blog post explains why putting datacenters in space is a really bad idea in case you thought about it. Another blog post also explains why AI datacenters in space are a bad idea. On a related topic, Margo Anderson discusses in IEEE Spectrum the increased saturation of the low orbits that are used by constellations like Starlink.
There are more and more airplanes that provide Internet connectivity. Thomas Dreibholz provides detailed measurements of the performance of his connection on a transatlantic flight.
The Internet Engineering Task Force (IETF) held its first meeting forty years ago in San Diego. There were 21 participants. Today more than 8000 people participate to the IETF.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>Simon Leinen discusses Packet trimming, a technique that emerged from research and now appears in datacenter.
Cloudlfare provides more information about the TCP connections that they observe in their network in a blog post
Philipp Tiesel has developed a new interactive website that allows companies to verify that their websites fully work for IPv6-only clients. Try it out at https://webres6.dev.sap
The IPv6 specification is now 30 years old, much older than the students who follow the networking courses.
Andra Lute describes briefly how roaming works among cellular network operators
Ookla provides interesting information about the performance of mobile networks in UK
John Kristoff and Max Resing discuss attacks on DNS root servers
Linux kernel developers rely on email to exchange patches to build the next version of the kernel. However, this email-based workflow is getting more and more fragile according to a recent update by Konstantin Ryabitsev.
Zi-Li Meng and his colleagues show that a student equipped with AI glasses can achieve excellent grades at a networking exam without any prior knowledge. They help students to answer exam questions. See https://xg.glass/posts/network-exam-test/
A detailed description of Kimwolf, an emerging Android TV botnet that has already infected more than 1.8 million devices and can be used to launch DDoS attacks, is available.
Cloudflare published its state of the Internet report for 2025.It provides many graphs showing the evolution of the web as seen from Cloudflare with metrics such as the adoption of the different versions of HTTP, IPv4 versus IPv6, the most popular browsers, but also the growth of AI bot traffic.
Netflix’s video streaming service generates a large amount of Internet traffic. This blog post provides more details on the new video codecs used by Netflix.
What are the most popular Internet services ? Joao Tomé analyzes the DNS requests sent to the 1.1.1.1 DNS resolver to reveal the most popular domain names in various categories.
Let’s Encrypt provides a large fraction of the TLS certificates used on the Internet. This democratization of TLS certificates was possible thanks to the adoption of the ACME protocol. Christophe Brocas explains the evolution of this protocol in an interesting blog post
RFC9460 defined the HTTPS and SVBC DNS resource records in November 2023. More than two years later, Jan Schaumann discusses the support for these records by different browsers.
A new edition of the book The Data Center as a Computer - Designing Warehouse-Scale Machines by Luiz André Barroso , Urs Hölzle, and Parthasarathy Ranganathan has been published as an open book. This is a recommended reading if you wish to understand the design principles of Google’s datacenters.
Andrew Cooks explains how to use tshark to detect various types of problems when streaming video over TCP.
The Ultra Ethernet specification describes how Ethernet can be enhanced to support datacenters that need to support large AI or HPC workloads. A recent arXiv report describes the main principles of this new technology. The authors also presented a two-hour tutorial on this topic.
Antonio Prato has released a website, https://ping6.it/ which allows one to compare the latency over IPv6 and IPv4 from multiple vantage points to reach a given destination.
2026 could be the year when wireless mesh networks from different vendors become interoperable thanks to the Thread 1.4 specification that unifies wireless mesh approaches.
ttl is a modern replacement for traceroute that collects multiple metrics.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>XKCD published a nice comic illustrating ping with ICMP Echo request and Echo response.
Larry Peterson discusses his views on how the next generation of networking students should be educated in an interesting blog post
The RFC Editor has published RFC9868 which introduces a format for UDP options. This is an exercise in extending a very simple and old protocol like UDP. Despite the fact that the document is standards track, it is unlikely that it will be widely deployed.
Brian Krebs published an interesting article on his blog discussing the new Aisuru botnet and its DDoS capabilities.
Amazon Web Services had an outage on October 19th and 20th, 2025. Many web services became unusable during this period. AWS hosts a large number of services used y web sites and provides DNS services. A 2024 study predicted that 25% of the top 10,000 web sites would be affected by a failure of AWS. Dan Goodin provides some details about the failure in an article published by arts.technica. Luke Kehoe discusses the impact of the failure based on data from downdetector notably. AWS has published some technical details about the outage.
Generative AI applications have attracted millions of users world wide. A recent technical report analyzes 60 hours of packet traces collected on smartphones using ChatGPT, CoPilot and Gemini. They reveal different communication patterns and different protocols. All applications use TLS, but Gemini is the only one to use QUIC.
The HTTP protocol provides numerical status codes in response to each request. The https://http.pizza/ web site provides an image with a pizza which can be used as a way to provide additional information about the status codes. It also provides additional information about the status code leveraging https://http.dev/. A nice way to illustrate HTTP status codes.
ARCEP, the French telecommunication regular, published a very interesting study carried out by Plum that analyzes the deployment of optical fiber in France, taking into account the technical and the economical aspects. The report clearly explains the problems faced when deploying fiber and provides interesting statistics.
The US government could ban TP-Link from selling access routers in the US. In the US, most home users buy their own access router. By providing cheap prices, TP-Link, a Chinese company, has captured more than one third of the US market. Although the US government seems to be worrying that these routers could be used by state-sponsored hackers, the main problem with access routers is that they need to be correctly configured, maintained by upgraded when vulnerabilities are discovered. There is an interesting tussle to be discussed. In some countries, access routers are provided by the ISPs that manage and upgrade them. These ISPs have the expertise to manage the access routers of their customers and can react when problems occur. Unfortunately, this can limit innovation as ISPs will typically only deploy a few types of access routers that they manage and rent to their customers. On the other hand, the US model where each home user selects his/her access router could in theory encourage innovation since many brands can provide access routers. Unfortunately, home users often tend to keep their old access routers for (too) many years and have difficulties in managing them correctly. Which is the best approach ? User-controlled access routers which can be old and insecure ? ISP-controlled access-routers which will be more secure but might not evolve as expected by some users…
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>The BurningMan festival attracts more than 70,000 attendees during 9 days in the Nevada desert. A growing number of these attendees bring Internet connectivity with them. An Ookla study reveals that this year the festival attendees had a significant impact on the performance of Starlink in the region.
Several cuts affected optical fibres in the Red Sea recently. Doug Madory analyzes in a blog post the impact of the failures on latencies in several cloud services and also on BGP routing.
Distributed denial of service attacks continue to grow, unfortunately. In early September, an attack reaching 1.5 billion packets per second coming from IoT devices and CPE in 11,000 different networks was detected. Later, Cloudflare announced a new record for DDoS. They suffered an attack that peaked at 22.2 Tbps and 10.6 billion packets per second but lasted only 40 seconds.
Linux powers most Internet servers, Android smartphones, and many IoT devices. Jonathan Corbet, who leads LWN.net, provides a nice overview of the evolution of Linux and its ecosystem during the last three decades in a one-hour-long video containing lots of interesting details.
In an interesting article published by IEEE Spectrum, William Webb questions the quest for more and more bandwidth in access networks. The new generation of cellular technologies has brought higher bandwidth with each generation. Will we need even more bandwidth for 6G?
Today, cellular networks allocate one IP address to each smartphone. This will probably change in the coming months/years as Lorenzo Colitti and Patrick Rohr have announced that Android 11+ will include support for DHCPv6 prefix delegation. This will enable network providers to delegate a /64 IPv6 prefix to each smartphone, which will be able to act as a real router and serve other devices connected using Wi-Fi or other wireless technologies such as 802.15.4.
At the end of September 2025, America Online (AOL) has stopped its dial-up service. AOL was a giant during the Internet bubble in the late 1990s and was later replaced by ISPs and telecommunication providers offering various Internet access solutions. An IEEE Spectrum article summarises the last years of this service and reminds the young students of the era of dial-up modems.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>The first service is the echo service defined in RFC862. When a client connects to the server using TCP, the server echoes all the bytes sent by the client over the TCP connection.
Students can test this service using telnet, netcat/nc or even curl.
nc echo.computer-networking.info 7
Hello
Hello
^C
curl telnet://echo.computer-networking.info:7
Hello
Hello
RFC862 also defines this service for UDP, but blindly echoing UDP messages is risky from a security viewpoint.
We also support the Discard protocol defined in RFC863. This service simply accepts TCP connections or UDP messages on port 9 and simply discards them without any reply.
nc discard.computer-networking.info 9
Hello
^C
And for UDP:
nc -u discard.computer-networking.info 9
hello
another
The last service is the daytime protocol specified in RFC867. This service simply accepts TCP connections and returns the time of the day on the server. It uses port 13 by default. For security reasons, we disable the UDP service.
nc daytime.computer-networking.info 13
08 SEP 2025 13:44:50 UTC
These services will be used by examples in the fourth edition of the Computer Networking: Principles, Protocols, and Practice ebook.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols, and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on Mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>Webservers suffer from the load caused by AI bots that try to collect has many data as possible to train their models. An entire session of the MAPRG working group at the IETF was dedicated to this problem. Wikipedia suffers a lot from these bots. In a blog post, Andrew Chan shows that it is possible to collect one billion web pages in 24 hours for a cost of 580 US$… The surge of AI bots is unlikely to stop soon… In the mean time, Cloudflare announced an AI labyrinth to trap misbehaving AI bots.
In an interesting blog post, Jan Schaumann clearly explains how web servers can be configured to encourage clients to use a specific version of HTTP.
David Redekop describes on the ADAM blog many of the popular utilizations of the DNS TXT records. Unfortunately, some of these records are also used to distribute malware. Another analysis of the DNS TXT records appeared on the RIPE blog in 2023.
Another less used DNS record is the LOC record that provides location information. A blog post shows that you can query the LOC record of where-is-the-iss.dedyn.io to find the current location of the International Space Station.
dig +short where-is-the-iss.dedyn.io LOC
51 34 44.060 S 18 40 22.060 W 431570.00m 10000m 10000m 10000m
On July 24, 2025, Starlink suffered from an outage. The ThousandEyes blog explores this outage from Internet data and reveals some interesting information about the Starlink network.
Denial of Service attacks continue to grow. The last reported peak attack used 7.3 Tbps of traffic.
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>
You can find his scripts on Github
This blog aims at encouraging students who read the open Computer Networking: Principles, Protocols and Practice ebook to explore new networking topics. You can follow this blog by subscribing to its RSS feed or by following @cnp3_ebook on mastodon. Feel free to share the posts that you find interesting on your preferred social network.
]]>The previous editions of Computer Networking: Principles, Protocols and Practice used a mixed approach, starting from the principles and then exploring the Internet protocols. Our students expressed some frustration with this approach as it forced them to wait several weeks before studying real protocols.
During the last two years, we adopted a different approach which seems to work pretty well with our students. The course is now divided into two main parts:
We have prepared a set of slides that follow this approach and work well with our students.
The next step is now to convert this organization into an ebook which is reusable by various universities. In the meantime, the slides are already available through the above links.
Suggestions and comments on this approach are more than welcome !
]]>