When implementing NTP servers, it’s always an interesting part to check whether the server is “up and running” and reachable from the clients. While I’ve done many basic NTP checks out of Linux, I lacked a small docu to do this with Windows. It turned out that there’s no need for third-party software because Windows already includes a tool to test NTP connections: w32tm.
During my IPv6 classes, I discovered a (minor) bug at the NGFW from Palo Alto Networks: ICMPv6 error messages, such as “time exceeded” (type 3) as a reply of traceroute, or “destination unreachable” (type 1) as a reply of a drop policy, are not correctly sourced from the IPv6 address of the data interface itself, but from the unspecified address “::”. Here are some details:
Continue reading Minor Palo Bug: ICMPv6 Errors sourced from Unspecified Address
Als netzwerktechnisches Spielkind beschäftige ich mich nicht nur mit den Netzwerken großer Firmenumgebungen, sondern auch mit meinem eigenen Anschluss daheim. Vor vielen Jahren habe ich dem echten Dual-Stack Anschluss der Deutschen Telekom mal auf die Finger geguckt – heute ist die Variante der Deutschen Glasfaser an der Reihe, welches zwar ein Dual Stack, aber ohne eigene öffentliche IPv4 Adresse ist. Quasi ein halbes DS-Lite. Kernfrage für mich war: Kann ich die Fritzbox (mit ihren mitgelieferten Presets für verschiedene ISPs) durch eine echte Enterprise-Firewall ersetzen, die ja leider nicht unbedingt alle Sprecharten wie PPPoE im Subinterface oder PPP IPv6CP unterstützen.
TL;DR: DHCP, DHCPv6-PD, RA.
For the last few years, I have been confused about Palo Alto NGFWs’ various options for configuring an IPv6 address on a layer 3 interface. Let’s have a look at some details:
Continue reading Palo Alto NGFW: Handling of IPv6 on the Interface
Meinberg, with the great help of Mr Weber, has implemented “syslog over TLS” in the LTOS version 7.06. The following report describes the general advantages of “syslog over TLS” and the implementation of it in the LTOS.
Continue reading Meinberg LTOS: “syslog-ng” and the Observed Implementation Pitfalls
More and more security-related devices are capable of sending syslog messages via an encrypted TLS channel. So does the well-known Meinberg LANTIME NTP server with its “LTOS” operating system. (And all the other LTOS-based NTP servers like the IMS or SyncFire series.) Here’s how you can configure it:
For my IPv6 training classes, I was missing a capture of a stateful DHCPv6 address assignment. That is: M-flag within the RA, followed by DHCPv6 messages handing out an IPv6 address among others. Therefore, I set up a DHCPv6 server on an Infoblox grid and furthermore used a Palo Alto NGFW as a DHCPv6 relay to it. I captured on two points: from the client’s point of view (getting to the relay) and from the server’s point of view (unicast messages from the relay). And since I was already there anyway, I additionally captured the same process for DHCPv4. So, here we go:
Continue reading Stateful DHCPv6 Capture (along with Relaying)
For administrative purposes, SSH is used quite often. Almost everyone in IT knows it. Keywords: OpenSSH, simply using “ssh <hostname>” on your machine, PuTTY for Windows, username + password or public key authentication, TCP port 22, simple firewall rules, ignoring the fingerprints ?♂️, SCP and SFTP. That’s it – basically.
However, it gets much more complicated if you look into the details. You have to deal with many different types and representations of fingerprints, as well as crypto algorithms. Troubleshooting specific connection problems is challenging.
To get an overview of your SSH server’s configuration is to scan them with appropriate tools. I’m showing two of them here: ssh_scan and the Nmap script “ssh2-enum-algos“.
Again two more commonly used network protocols for the Ultimate PCAP: the Remote Authentication Dial-In User Service (RADIUS) and the Terminal Access Controller Access-Control System Plus (TACACS+) protocols. Captured with quite some details:
At SharkFest’22 EU, the Annual Wireshark User and Developer Conference, I attended a beginners’ course called “Network Troubleshooting from Scratch”, taught by the great Jasper Bongertz. In the end, we had some high-level discussions concerning various things, one of them was the insight that TCP RSTs are not only sent from a server in case the port is closed, but are also commonly sent (aka spoofed) from firewalls in case a security policy denies the connection. Key question: Can you distinguish between those spoofed vs. real TCP RSTs? Initially, I thought: no, you can’t, cause the firewalls out there do a great job.
It turned out: you can!
In general, Network Address Translation (NAT) solves some problems but should be avoided wherever possible. It has nothing to do with security and is only a short-term solution on the way to IPv6. (Yes, I know, the last 20 years have proven that NAT is used everywhere every time. ?) This applies to all kinds of NATs for IPv4 (SNAT, DNAT, PAT) as well as for NPTv6 and NAT66.
However, there are two types of NATs that do not only change the network addresses but do a translation between the two Internet Protocols, that is IPv4 <-> IPv6 and vice versa. Let’s focus on NAT46 this time. In which situations is it used and why? Supplemented by a configuration guide for the FortiGates, a downloadable PCAP and Wireshark screenshots.
Continue reading Accessing IPv6-only Resources via Legacy IP: NAT46 on a FortiGate
The other day I just wanted to capture some basic Linux traceroutes but ended up troubleshooting different traceroute commands and Wireshark display anomalies. Sigh. Anyway, I just added a few Linux traceroute captures – legacy and IPv6 – to the Ultimate PCAP. Here are some details:
Fortunately, there was a SharkFest – the “Wireshark Developer and User Conference” – this year in Europe again. I was there and gave an IPv6 Crash Course likewise. Yeah! It’s my favourite topic, you know. 75 minutes full of content, hence the name crash course.
Here are my slides as well as the video recording. If you want a crash course for IPv6, here we go:
From time to time I stumble upon Tweets about counting the number of IPv6 addresses (1 2 3). While I think it is ok to do it that way when you’re new to IPv6 and you want to get an idea of it, it does not make sense at all because the mere number of IPv6 addresses is ridiculously high and only theoretically, but has no relevance for the real-world at all. Let me state why:
For some reason, I came across a blog post by Gian Paolo called Small servers. This reminded me of some fairly old network protocols (that no one uses as far as I know) that are not in my Ultimate PCAP yet. Hence I took some minutes, captured them, and took some Wireshark screenshots. They are: echo, discard, daytime, chargen, and time. Mostly via TCP and UDP, and, as you would have expected, IPv6 and legacy IP.
I’m aware that this is not of interest to most of you. :) But for the sake of completeness, and because I love adding new protocols to the Ultimate PCAP, I added them though.