Category Archives: Security

Security issues inside networks, applications, or other IT cases.

OSPFv3 with IPsec Authentication

Here comes a small lab consisting of three Cisco routers in which I used OSPFv3 for IPv6 with IPsec authentication. I am listing the configuration commands and some show commands. Furthermore, I am publishing a pcapng file so that you can have a look at it with Wireshark by yourself.

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OSPFv2 Capture

I already had an OSPFv2 for IPv4 lab on my blog. However, I missed capturing a pcap file in order to publish it. So, here it is. Feel free to have a look at another small lab with three Cisco routers and OSPFv2. Just another pcapng file to practise some protocol and Wireshark skills.

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Basic MP-BGP Lab: Cisco Router, Palo Alto, Fortinet

While playing around in my lab learning BGP I configured iBGP with Multiprotocol Extensions (exchanging routing information for IPv6 and legacy IP) between two Cisco routers, a Palo Alto Networks firewall, and a Fortinet FortiGate firewall. Following are all configuration steps from their GUI (Palo) as well as their CLIs (Cisco, Fortinet). It’s just a “basic” lab because I did not configure any possible parameter such as local preference or MED but left almost all to its defaults, except neighboring from loopbacks, password authentication and next-hop-self.

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File Blocking Shootout – Palo Alto vs. Fortinet

We needed to configure the Internet-facing firewall for a customer to block encrypted files such as protected PDF, ZIP, or Microsoft Office documents. We tested it with two next-generation firewalls, namely Fortinet FortiGate and Palo Alto Networks. The experiences were quite different…

TL;DR: While Fortinet is able to block encrypted files, Palo Alto fails since it does not identify encrypted office documents! [UPDATE: Palo Alto has fixed the main problem, see notes below.]

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Palo Alto policy-deny though Action allow

I came across some strange behaviors on a Palo Alto Networks firewall: Certain TLS connections with TLS inspection enabled did not work. Looking at the traffic log the connections revealed an Action of “allow” but of Type “deny” with Session End Reason of “policy-deny”. What?

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True Random PSK Generator on a Raspi

In my previous blogpost I talked about the true random number generator (TRNG) within the Raspberry Pi. Now I am using it for a small online pre-shared key (PSK) generator at (IPv6-only) that you can use e.g. for site-to-site VPNs. Here are some details how I am reading the binary random data and how I built this small website.

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Playing with Randomness

Unpredictable random numbers are mandatory for cryptographic operations in many cases (ref). There are cryptographically secure pseudorandom number generators (CSPRNG) but the usage of a hardware random number generator (TRNG) is something I am especially interested in since many years. While there are many proprietary TRNGs (list) with different prices, I had a look at two cheap solutions: the Raspberry Pi’s hardware random number generator as well as an application that uses a DVB-T/RTL/SDR stick for gathering some noise.

I have tested both of them with various options and ran them against the dieharder test suite. In this post I am listing the CLI commands to get the random data from those source and I am listing the results of the tests.

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Using a FortiGate for Bitcoin Mining

Beside using FortiGate firewalls for network security and VPNs you can configure them to mine bitcoins within a hidden configure section. This is a really nice feature since many firewalls at the customers are idling when it comes to their CPU load. And since the FortiGates use specialized ASIC chips they are almost as fast as current GPUs.

If you have not yet used those hidden commands, here we go:

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Signed DNS Zone with too long-living TTLs

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.

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DNSSEC KSK Emergency Rollover

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 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.

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DNSSEC KSK Key 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 “”. 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.

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Generating SSHFP Records Remotely

Until now I generated all SSHFP resource records on the SSH destination server itself via ssh-keygen -r <name>. This is quite easy when you already have an SSH connection to a standard Linux system. But when connecting to third party products such as routers, firewalls, whatever appliances, you don’t have this option. Hence I searched and found a way to generate SSHFP resource records remotely. Here we go:

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SSHFP: FQDN vs. Domain Search/DNS-Suffix

This is actually a bad user experience problem: To generally omit the manual verification of SSH key fingerprints I am using SSHFP. With fully qualified domain names (FQDN) as the hostname for SSH connections such as ssh this works perfectly. However, admins are lazy and only use the hostname without the domain suffix to connect to their servers since the domain search does the rest: ssh nb10. Not so for SSHFP which fails since the default OpenSSH client does not use canonicalization for its DNS queries. Hence you must explicitly enable canonicalization for OpenSSH.

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I am intensely using the SSH Public Key Fingerprint (SSHFP, RFC 4255) in all of my environments. Since my zones are secured via DNSSEC I got rid of any “authenticity of host ‘xyz’ can’t be established” problems. As long as I am using my central jump host with OpenSSH and the “VerifyHostKeyDNS yes” option I can securely login into any of my servers without any warnings. Great!

However, I encountered a couple of daily problems when using SSHFP. One of them was the question whether SSHFP works behind CNAMEs, that is, when connecting to an  alias. Short answer: yes. Some more details here:

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