Category Archives: Internet Access

Posts concerning xDSL/fiber/cable Internet connections, merely for private usage. In Germany, these are the ISPs such as 1&1, Deutsche Telekom, Kabel Deutschland.

iPad Ping: WLAN vs. LAN

Meine Kids spielen derzeit häufig Brawl Stars, ein Echtzeit Onlinespiel. Und sie schauen auch immer mal Videos dazu, bei denen ihnen jetzt der Floh ins Ohr gesetzt wurde, dass man ein iPad ja auch per LAN-Adapter mit einem Netzwerkkabel ausstatten kann, was ja den Ping verbessert.

JAAAA, endlich waren meine Kenntnisse in Sachen Netzwerktechnik mal von meinen Kindern gefragt. “Papa, weißt du, was ein LAN-Kabel ist?” “Ja klar.” “Hast du so eines?” “Ja, circa Hundert.” “Waaas? Echt jetzt? Dann muss ich mir ja gar keins kaufen.” 😂

Neben der Subjektivität, ob das Zocken per LAN-Kabel jetzt merklich besser wird, wollte ich mal objektiv messen, wie sich die Latenz eines per Ethernet-Adapter angeschlossenen iPads denn nun wirklich verhält. Wie viel besser wird der Ping im Idle- bzw. im Volllastfall? Was sagt die Laufzeit zum Default Gateway? Hier ein paar Tests:

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Misusing Palo’s Captive Portal as a Guest Wi-Fi Welcome Page

I was faced with an interesting customer requirement: An existing guest Wi-Fi should be prefaced with a welcome page for accepting the terms and conditions. Since there was already a Palo Alto Networks firewall in place, could we perhaps use its captive portal directly for this purpose? It’s not about authenticating the users, but only for a single webpage with a simple check button that should appear once a month per device.

TL;DR: While we were able to redirect every device to a welcome page, we were not able to extend the lifetime of those sessions to longer than 24 hours. This might fit for short-term guest Wi-Fis, but is not appropriate for long-term connections aka BYOD. However, this is how we have done it:

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Dynamic DNS on a Palo

With PAN-OS 9.0 (quite some time ago), Palo Alto Networks has added Dynamic DNS for a firewall’s interfaces. That is: If your Internet-facing WAN interface gets a dynamic IP address via DHCP or PPPoE (rather than statically configured), the firewall updates this IP address to a configured hostname. The well-known DynDNS providers such as Dyn (formerly DynDNS), No-IP, or FreeDNS Afraid are supported. Since the Palo supports DHCP, PPPoE (even on tagged subinterfaces) as well as DHCPv6 respectively PPPoEv6, we can now operate this type of firewall on residential ISP connections AND still access it via DNS hostnames. Great. Let’s have a look at the configuration steps.

Spoiler: The DynDNS feature on a Palo only supports static IPv6 addresses rather than dynamic ones. 🤦🤦🤦 Yes, you haven’t misread. The DYNAMIC DNS feature does not support DYNAMIC IP addresses, but only STATIC ones. D’oh!

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Optimized NAT46 Config on a FortiGate

Johannes published a basic NAT46 configuration for a Fortigate firewall with FortiOS 7.0 some time ago. I run such a service (legacy IPv4 access to IPv6-only resources) since FortiOS 5.6, which means more than six years; lastly with FortiOS 6.4. It’s running for more than 100 servers without any other problems as we see them with IPv4 only or dual stack services.

But we weren’t happy with the basic configuration example by Fortinet. We wanted some NAT46 sample configuration with more details, that is: including the original source IPv4 address within the synthesized/SNATted IPv6 address. More in this post, after a short story about my way to a running nat46 configuration with port forwarding in FortiOS 7.2.x.

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Verbindungsaufbau Deutsche Glasfaser

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.

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Accessing IPv6-only Resources via Legacy IP: NAT46 on a FortiGate

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.

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#heiseshow: IPv6 setzt sich langsam durch – die wichtigsten Fragen

Ich durfte zu Gast bei der #heiseshow zum Thema IPv6 sein. In Anlehnung an die Artikelserie über IPv6 in der c’t 7/2022, in der auch mein Artikel über die Vorteile von IPv6-Adressen erschienen ist, ging es bei diesem Video-Podcast um gängige Fragen zu IPv6 sowohl im Heimanwender- als auch im Enterprise-Segment. Ne knappe Stunde lief die Schose und ich empfand es als ziemlich kurzweilig. ;)

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Pi-hole Installation Guide

You probably know already the concept of the Pi-hole. If not: It’s a (forwarding) DNS server that you can install on your private network at home. All your clients, incl. every single smartphone, tablet, laptop, and IoT devices such as smart TVs or light bulb bridges, can use this Pi-hole service as their DNS server. Now here’s the point: it not only caches DNS entries, but blocks certain queries for hostnames that are used for ads, tracking, or even malware. That is: You don’t have to use an ad- or track-blocker on your devices (which is not feasible on smart TVs or smartphone apps, etc.), but you’re blocking this kind of sites entirely. Nice approach!

Yes, there are already some setup tutorials for the Pi-hole out there. However, it’s not only about installing the mere Pi-hole, but setting it up with your own recursive DNS server (since the default installation forwards to public DNS servers), using DNSSEC, and adding some more adlists. That’s why I am listing my installation procedure here as well. However, it’s not a complete beginners guide. You’ll need some basic Linux know-how.

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iperf3 on a FortiGate

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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2001:db8::/32 in the Wild

If you have ever read some docs or RFCs about IPv6 you should be quite familiar with the 2001:db8::/32 “IPv6 Address Prefix Reserved for Documentation”, RFC 3849. This RFC clearly states how you should handle addresses within this range: “This assignment implies that IPv6 network operators should add this address prefix to the list of non-routeable IPv6 address space, and if packet filters are deployed, then this address prefix should be added to packet filters.”

I was interested whether those addresses are actually used in the Internet. For this purpose I analyzed my firewall logs for 6 months to get an idea. Though it was not that much, I actually got a couple of connections inbound and outbound (!) sourced or destined to those reserved IPv6 addresses.

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Internet’s Noise

If you are following the daily IT news you have probably seen many articles claiming they have scanned the whole Internet for this or that. Indeed there are tools such as the ZMap Project “that enable researchers to perform large-scale studies of the hosts and services that compose the public Internet”.

This time I was not interested in scanning something, but in the question about “how many scans happen during one day on my home ISP connection?” Or in other words: What is the Internet background noise as seen by almost any customer? For this I sacrificed my Internet connection at home for 24 hours, while a factory-resetted router established a fresh Internet connection (IPv6 & IPv4) without any end devices behind it. No outgoing connections that could confuse or trigger any scans. That is: All incoming connections are really unsolicited and part of some third-party port scans, worm activities, or whatever. Using a network TAP device I captured these 24 hours and analyzed them with Wireshark.

In this blogpost I will present some stats about these incoming port scans. Furthermore I am publishing the pcap file so you can have a look at it by yourself.

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TROOPERS18: Dynamic IPv6 Prefix Problems and VPNs

Just a few days ago I gave a talk at Troopers 18 in Heidelberg, Germany, about the problems of dynamic (non-persistent) IPv6 prefixes, as well as IPv6 VPNs in general. Following are my slides and the video of the talk:

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Internetanschlusswechsel innerhalb der Telekom: Ein Albtraum

Anstelle von technischen Details heute mal ein Erfahrungsbericht. Vielleicht sollte ich eher sagen: ein Odysseebericht. Für einen meiner Kunden habe ich den Business-Internetanschluss umgezogen. “Einfache Sache”, so dachte ich anfangs, zumal der alte und neue Anschluss beide bei dem gleichen Anbieter liegen: der Telekom. Von einem “Company Connect” der T-Systems (ok, doch nicht exakt Telekom) hin zu einem DeutschlandLAN Connect IP.

Es war fürchterlich:

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Detect DNS Spoofing: dnstraceroute

Another great tool from Babak Farrokhi is dnstraceroute. It is part of the DNSDiag toolkit from which I already showed the dnsping feature. With dnstraceroute you can verify whether a DNS request is indeed answered by the correct DNS server destination or whether a man-in-the-middle has spoofed/hijacked the DNS reply. It works by using the traceroute trick by incrementing the TTL value within the IP header from 1 to 30.

Besides detecting malicious DNS spoofing attacks, it can also be used to verify security features such as DNS sinkholing. I am showing the usage as well as a test case for verifying a sinkhole feature.

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RTTs with different ISPs

Just a short post this time, but an interesting fact concerning different Internet Service Providers (ISPs) and their routing to/from other countries. I have a customer in Germany that has a remote office in France, connected via a site-to-site VPN. Around April last year the french office decided to change the ISP to a cheaper competitor that offers the same speed/bandwidth and therefore has no disadvantages… Well, I disagree.

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