It’s not always this simple DNS thing such as “single query – single answer, both via UDP”. Sometimes you have some more options or bigger messages that look and behave differently on the network. For example: IP fragmentation for larger DNS answers that do not fit into a single UDP datagram (hopefully not after the DNS flag day 2020 anymore), or DNS via TCP, or some newer options within the EDNS space such as “EDNS Client Subnet” (ECS) or DNS cookies.
I won’t explain any details about those options, but I am publishing a pcap with that kind of packets along with some Wireshark screenshots. Feel free to dig into it.
Continue reading DNS Capture: UDP, TCP, IP-Fragmentation, EDNS, ECS, Cookie
This post is not about software but hardware tools for network admins. Which network gadgets am I using during my daily business? At least three, namely the Airconsole, the Pockethernet and the ProfiShark, which help me in connecting to serial ports, testing basic network connectivity, and capturing packets in a high professional way. Come in and have a look at how I’m working.
Continue reading My Network Gadgets
I was interested in how a recursive DNS server resolves DNS queries in detail. That is, not only the mere AAAA or A record, but also DNSSEC keys and signatures, the authority and additional section when testing with
dig , and so on. For this I made two simple DNS queries to my recursive DNS server which resulted in more than 100 DNS packets at all. Wow.
In the following I am publishing a downloadable pcap so that you can analyse it by yourself. Furthermore I am showing some listings and screenshots to get an idea of the DNS resolution process.
Continue reading Single DNS Query – Hundreds of Packets
If you’re following my blog you probably know that I am using IPv6 everywhere. Everything in my lab is dual-stacked if not already IPv6-only. Great so far.
A few months ago my lab moved to another ISP which required to change all IP addresses (since I don’t have PI space yet). Oh boy! While it was almost no problem to change the legacy IPv4 addresses (only a few NATs), it was a huge pain in the … to change the complete infrastructure with its global unicast IPv6 addresses. It turned out that changing the interface IPv6 addresses was merely the first step, while many modifications at different services were the actual problem. And this was *only* my lab and not a complex company or the like.
Following you find a list of changes I made for IPv6 and for legacy IP. Just an overview to get an idea of differences and stumbling blocks.
Continue reading IPv6 Renumbering: A Pain in the …
Some time ago I published a pcap that can be used to study basic IPv6 protocol messages such as ICMPv6 for Router Advertisements, Neighbor Solicitations, etc.: “Basic IPv6 Messages: Wireshark Capture“. You can use it to learn the basic IPv6 address assignment and layer 2 address resolution. However, that pcap does not include any upper layer protocols.
This time I captured a few application layer protocols that I used over IPv6 rather than over legacy IP. Common user protocols such as DNS, HTTP/S, IMAP, SMTP, as well as some network administration protocols: SSH, SNMP, and Ping. It is not that interesting at all ;) though you can use it to have some examples for Wireshark to prove that those application protocols are almost the same when run above IPv6 compared to IPv4.
Continue reading IPv6 Upper Layer Protocol Samples
Implementing DNSSEC for a couple of years now while playing with many different DNS options such as TTL values, I came around an error message from DNSViz pointing to possible problems when the TTL of a signed resource record is longer than the lifetime of the DNSSEC signature itself. Since I was not fully aware of this (and because I did not run into a real error over the last years) I wanted to test it more precisely.
Continue reading Signed DNS Zone with too long-living TTLs
In my last blogpost I showed how to perform a DNSSEC KSK rollover. I did it quite slowly and carefully. This time I am looking into an emergency rollover of the KSK. That is: What to do if your KSK is compromised and you must replace it IMMEDIATELY.
I am listing the procedures and commands I used to replace the KSK of my delegated subdomain
dyn.weberdns.de with BIND. And as you might already suggest it, I am showing DNSViz graphs after every step since it greatly reveals the current DNSKEYs etc.
Continue reading DNSSEC KSK Emergency Rollover
Probably the most crucial part in a DNSSEC environment is the maintenance of the key-signing key, the KSK. You should rollover this key on a regular basis, though not that often as the zone signing keys, the ZSKs. I am doing a KSK rollover every 2 years.
In the following I will describe the two existing methods for a KSK rollover along with a step-by-step guide how I performed such a rollover for my zone “weberdns.de”. Of course again with many graphics from DNSViz (with “redundant edges”) that easily reveal the keys and signatures at a glance.
Note that this blogpost is NOT about the Root Zone KSK Rollover
that appears in 2017/2018. It is merely about your OWN zone
that is secured via DNSSEC.
Continue reading DNSSEC KSK Key Rollover
If you are already familiar with DNSSEC this is quite easy: How to sign a delegated subdomain zone. For the sake of completeness I am showing how to generate and use the appropriate DS record in order to preserve the chain of trust for DNSSEC.
Continue reading Signing a Delegated Subdomain
If you’re running your own DNS resolver you’re probably interested in some benchmark tests against it, such as: how fast does my own server (read: Raspberry Pi) answer to common DNS queries compared to 184.108.40.206.
In this blogpost I am showing how to use two tools for testing/benchmarking DNS resolvers: namebench & dnseval. I am listing the defaults, giving some hints about them and showing examples in which I tested some private and public DNS resolvers: a Fritzbox router, a Raspberry Pi with Unbound, Quad9, OpenDNS, and Google Public DNS.
Continue reading Benchmarking DNS: namebench & dnseval
Just a quick glance at the domain_analyzer script from Sebastián García and Verónica Valeros. “Domain analyzer is a security analysis tool which automatically discovers and reports information about the given domain. Its main purpose is to analyze domains in an unattended way.” Nice one. If you’re running your own DNS servers you should check e.g. whether your firewall rules are correct (scanned with Nmap) or whether you’re not allowing zone transfer, etc.
Continue reading All-in-One DNS Tool: Domain Analyzer
I am testing a lot with my own DNS servers as well as with third-party DNS implementations such as DNS proxies on firewalls, DNSSEC validation on resolvers, etc. While there are a number of free DNS online tools around the Internet I was lacking some DNS test names with certain properties or resource records. Hence I configured a couple of them on my own authoritative DNS servers and its zone
For example we encountered a bug on the Palo Alto DNS proxy that has not stored the TTL value correctly – hence some test names with different TTL values. Or we had some problems when a single DNS name has more than 15 IPv4/IPv6 addresses – hence some test names with lots of addresses. And many more: Continue reading DNS Test Names & Resource Records
What is the biggest problem of PGP? The key distribution. This is well-known and not new at all. What is new is the OPENPGPKEY DNS resource record that delivers PGP public keys for mail addresses. If signed and verified with DNSSEC a mail sender can get the correct public key for his recipient. This solves both key distribution problems: 1) the delivery of the public key and 2) the authenticity of the key itself, i.e., that you’re using the correct key to encrypt a mail.
The “DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP” is specified in the experimental RFC 7929. Let’s have a look on how you can add your public key into the zone file of your DNS server.
Continue reading PGP Key Distribution via DNSSEC: OPENPGPKEY
I really like the kind of security features that are easy to use. The CAA “DNS Certification Authority Authorization” is one of those, specified in RFC 6844. As a domain administrator you must only generate the appropriate CAA records and you’re done. (Unlike other security features such as HPKP that requires deep and careful planning or DANE which is not used widely.) Since the check of CAA records is mandatory for CAs since 8. September 2017, the usage of those records is quite useful because it adds another layer of security.
Continue reading CAA: DNS Certification Authority Authorization
Haha, do you like acronyms as much as I do? This article is about the feature from Palo Alto Networks’ Next-Generation Firewall for Internet Protocol version 6 Neighbor Discovery Protocol Router Advertisements with Recursive Domain Name System Server and Domain Name System Search List options. ;) I am showing how to use it and how Windows and Linux react on it.
Continue reading PAN NGFW IPv6 NDP RA RDNSS & DNSSL