Category Archives: Network

Computer networks over IPv4 and IPv6. Switching, Routing, and Firewalling.

FortiGate bug: firewalls sending excessive requests to the NTP Pool

Fortinet, NTP, , , , , ,

The NTP Pool is a volunteer organization that provides time synchronization service to hundreds of millions of computers worldwide. A typical client might query a particular NTP Pool server ~10-60 times/hour. Wikipedia lists some abusive clients that far exceeded the normal rate. This wastes NTP server resources, may interfere with other clients, and can trigger DDoS protections. In late 2019, a software update made some FortiGate firewalls very unfriendly to the NTP Pool.

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NTS Published as Standard

Authentication, NTP, , , , ,

This is a guest blogpost by Martin Langer, Ph.D. student for “Secured Time Synchronization Using Packet-Based Time Protocols” at Ostfalia University of Applied Sciences, Germany.

The Internet Engineering Task Force (IETF) published the Network Time Security protocol (NTS) as RFC 8915 on October 1, 2020. This new standard offers security mechanisms for the widely used Network Time Protocol v4 (NTPv4), which has been operated mostly unsecured until now. After almost eight years of development, global collaboration, and many interoperability tests of leading NTP software developers, NTS represents a mature security protocol. In this post, I’ll give you a short overview of the development progress of NTS and provide a list of public implementations and NTS secured time servers…

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iperf3 on a FortiGate

Bandwidth/Delay, Fortinet, Internet Access, Monitoring, , , ,

This is a really nice feature: you can run iperf3 directly on a FortiGate to speed-test your network connections. It’s basically an iperf3 client. Using some public iperf servers you can test your Internet bandwidth; using some internal servers you can test your own routed/switched networks, VPNs, etc. However, the maximum throughput for the test is CPU dependent. So please be careful when interpreting the results. Here we go:

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NTP Filtering (Delay & Blockage) in the Internet

NTP, , , , , , , ,

NTP (Network Time Protocol) messages are sometimes rate-limited or blocked entirely by Internet operators. This little-known “NTP filtering” was put into place several years ago in response to DDoS (Distributed Denial of Service) attacks. NTP filtering may drop NTP messages based on rate or message size. Let’s dig into it: Continue reading NTP Filtering (Delay & Blockage) in the Internet →

A Little Printing Please – Packet Capture

iPhone/iPad, Network, , , , , ,

Uh, I wasn’t aware of so many different printing protocols. Do you? While I was trying to solve a little printing problem I took a packet capture of three different printing variants over TCP/IP: Raw via TCP port 9100, LPD/LPR via TCP port 515, and Apple’s AirPrint which uses the Internet Printing Protocol IPP. As always, you can download this pcap and have a look at it by yourself.

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Palo Alto GRE Tunnel

Network, Palo Alto Networks, , ,

Since PAN-OS version 9.0 you can configure GRE tunnels on a Palo Alto Networks firewall. Greetings from the clouds. As always, this is done solely through the GUI while you can use some CLI commands to test the tunnel. This time Palo put a little stumbling block in there as you have to allow a GRE connection with a certain zone/IP reference. I will show how to set up such a GRE tunnel between a Palo and a Cisco router. Here we go:

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UK IPv6 Council Spring 2020: Incorrect Working IPv6 Clients & Networks

Conference Talks, IPv6, NTP, , , , ,

I did a short presentation at the spring 2020 roundtable of the UK IPv6 Council. The talk was about a case study I did with my NTP server listed in the NTP Pool project: For 66 days I captured all NTP requests for IPv6 and legacy IP while analyzing the returning ICMPv6/ICMPv4 error messages. (A much longer period than my initial capture for 24 hours.) Following are my presentation slides along with the results.

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SharkFest’19 EUROPE: IPv6 Crash Course

Conference Talks, IPv6, , , , , ,

I gave a session about IPv6 at SharkFest’19 EUROPE, the annual Wireshark developer and user community conference, named “IPv6 Crash Course: Understanding IPv6 as seen on the wire“. The talk is about the IPv6 basics, which are: IPv6 addresses & address assignment, link-layer address resolution, and ICMPv6. Tips for using Wireshark coloring rules and display filters round things up.

As I have not yet published the slides, here they are. Unfortunately, we were not able to record the session due to technical problems. Neither the video nor the audio. ;( Hence, here are only mere slides.

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More Capture Details

Network, , , , , , , , , , , , , ,

In the previous post, I released my Ultimate PCAP which includes every single pcap I had so far on my blog. But that’s not all: I have some packets in there that were not yet published up to now. That is, here are some more details about those (probably well-known) protocols. These are:

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The Ultimate PCAP

Network, , , ,

For the last couple of years, I captured many different network and upper-layer protocols and published the pcaps along with some information and Wireshark screenshot on this blog. However, it sometimes takes me some time to find the correct pcap when I am searching for a concrete protocol example. There are way too many pcaps out there.

This is supposed to change now:

I’m publishing a single pcap meant to be a single point of source for Wireshark samples. It is summarizing *all* previous ones from my blog and even adding some more protocols and details. I will constantly add more packets to this pcap if I have some. Currently, it has > 60 different protocols and hundreds of variants, such as IPv6 and legacy IP traffic, different DNS query types, ICMP error codes, and so on.

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VoIP Captures

Network, , , , ,

VoIP calls, using the network protocols SIP/SDP and RTP, are the de-facto standard when it comes to voice calls. Wireshark offers some special features to analyze those calls and RTP streams – even with a nice “Play Streams” option, which discretely decodes your calls. Ouch. Again and again, frightening which privacy-related protocols are completely unencrypted on the Internet!

Here are some hints for Wireshark as well as a downloadable pcap with three calls in there. ;) Have fun!

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DNS Capture – The Records Edition

DNS/DNSSEC, , , , , , ,

Some time ago I published a post called DNS Test Names & Resource Records which lists many different FQDNs with lots of different RRs. You can use those public available DNS names to test your DNS servers or the like. However, I was missing a packet capture showing all these resource records as they appear on the wire. So now, here it is. If you are searching for some packets to test your tools for whatever reason, feel free to download this pcap.

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