A highly available WireGuard VPN setup

WireGuard is a communication protocol and free and open-source software that implements encrypted virtual private networks (VPNs), and was designed with the goals of ease of use, high speed performance, and low attack surface.

My Journey to WireGuard

I’ve been using it in my home lab setup since about 2020. When, in the end of 2021, it was finally merged into the Linux mainline with release 5.9, I started to replace my former Tinc-VPN setup with it. Tinc-VPN is another great open source VPN solution. Unfortunately, its development has stalled over the last years which motivated me to look for alternatives. In contrast to WireGuard, Tinc runs as a user-space daemon and uses tun/tap devices which adds a significant processing overhead. Like WireGuard, it is also using UDP for tunneling data, but falls back to TCP in situations where direct datagram connectivity is not feasible. Another big advantage of Tinc is its ability to form a mesh of nodes and to route traffic within it when direct P2P connections are not possible due to firewall restrictions. At the same time, this mesh is also used for facilitating direct connections by signaling endpoint addresses of NATed hosts.

Tinc’s mesh capability.

This mesh functionality made Tinc quite robust against the failure of single nodes as usually we could route traffic via other paths.

Highly Available WireGuard server setup

To counteract this shortcoming, this blog post will present a highly available WireGuard setup using the Virtual Router Redundancy Protocol (VRRP) as implemented by the keepalived daemon.

That said, it is worth noting that this setup does will not bring back some of the beloved features of Tinc. Both meshing, the peer and and endpoint discovery features of Tinc are currently and will never be supported by WireGuard. Jason A. Donenfeld the author of WireGuard focused the design of WireGuard on simplicity, performance and auditability. Hence advanced features like the ones mentioned will only be available to WireGuard by additional agents / daemons which control and configure WireGuard for you. Examples for such are Tailscale, Netmaker and Netbird.

The setup presented in this post is a so called active / standby configuration consisting of two almost equal configured Linux servers running both WireGuard and the keepalived daemon. As the name suggest only one of those two servers will by actively handling WireGuard tunneling traffic while the other one stands by for the event of a failure or maintenance of the active node.

VRRP Wireguard Setup


Before get started some requirements for the setup:

  • 2 Servers running Linux 5.9 or newer.
  • A working Wireguard configuration.
  • A local L2 network segment two which both servers are connected.
  • Upstream connectivity without NATing via gateway connected to the network segment (usually provided by your internet or hosting provider).
  • An unused address to be used as Virtual IP (VIP) which roamed between the two servers by VRRP.

An important point is here the assumption that we are running both servers in the same switched network segment as this is a requirement for VRRP. We are also assuming that the upstream gateway performs no NATing. This guide covers only IPv6 addressing. However all steps can be also adapted or repeated for a dual stack or IPv4-only setup.

Detailed steps

Here are some of the specifics for my setup which need to be adapted by you:

  • Server Key (same use by both servers)
    • Private: YIEDx+A2ONo5+uv3mrk/p7ileL3T5QQ8hleQK0IYEEI=
    • Public: XGubrkGtuECdvoykKeUiNMigk2onfLCPfEo9Im+vmx8=
  • Peer Key (In this example we only have a single peer)
    • Private: OIbpWVIVVBOtWfwkmXkFRN7Q/jBdfYtsGt7j97aHx1Q=
    • Public: 3NGl6gTOGs6ai0RE91VmVFgF+N4gw1EBG11KOeiKJAg=
  • Public Server Subnet: 2001:DB8:1::/64
    • Gateway: 2001:DB8:1::1
    • Virtual IP: 2001:DB8:1::2
    • Server A: 2001:DB8:1:::3
    • Server B: 2001:DB8:1::4
  • WireGuard Tunnel Subnet: 2001:DB8:2::1/64
    • Server: 2001:DB8:2::1 (same used by both servers)
    • Peer: 2001:DB8:2::2
  • Interface names
    • Wireguard: wg1
    • Upstream: eno1

1. Prepare servers

We start of preparing the two servers by installing WireGuard and keepalived:

sudo apt install keepalived wireguard-tools iproute2

Next we configure a WireGuard interface on both servers using exactly the same configuration file at /etc/wireguard/wg1.conf:

Address = 2001:DB8:2::1/64
PrivateKey = YIEDx+A2ONo5+uv3mrk/p7ileL3T5QQ8hleQK0IYEEI=
ListenPort = 51800

PublicKey = 3NGl6gTOGs6ai0RE91VmVFgF+N4gw1EBG11KOeiKJAg=
AllowedIPs = 2001:DB8:2::2/128
PersistentKeepalive = 25

Similarly, a reciprocal configuration file is needed on the client side which skip here for brevity. Before proceeding, we activate the interface on both servers:

systemctl enable --now wg-quick@wg1

wg show wg1 # Check if interface is up

2. Configuring Keepalived

Create a configuration file for keepalived at /etc/keepalived/keepalived.conf

global_defs {
    script_user root

# Check if the server the WireGuard interface configured
vrrp_script check_wg {
    script "/usr/bin/wg show wg1"
    user root

vrrp_instance wg_v6 {
    interface eno1
    virtual_router_id 52
    notify /usr/local/bin/

    state BACKUP # use BACKUP for Server B
    priority 99 # use 100 for Server B

    virtual_ipaddress {

    track_script {

Create a notification script for keepalived at /usr/local/bin/




case ${STATE} in
		ip link set up dev ${WGIF}

		ip link set down dev ${WGIF}

		echo "unknown state"
		exit 1

Now start the keepalived daemon:

chmod +x /usr/local/bin/
systemctl enable --now keepalived

4. Testing the fail over

In our configuration, Server A has a higher VRRP priority and as such will be preferred if both servers are healthy. To test our setup, we simply bring down the WireGuard interface on Server A and observe how the VIP gets moved to Server B. From the WireGuard peers perspective not much changes. In fact no connections will be dropped during the fail-over. Internally, the clients WireGuard interface renegotiate the handshake. However, that step is actually not observable by the user.

Run the following commands on Server A while alongside test the connectivity from the client side through the tunnel via ping -i0.2 2001:DB8:2::1:

# Check that keepalived has moved the VIP to interface eno1
ip addr show dev eno1

# Bring down the Wireguard interface
wg-quick down wg1

# Keepalived should now have moved the VIP to Server B
ip addr show dev eno1

Going further

In my personal network, I operate a Interior Gateway Protocol (IGP) to dynamically route traffic within and also towards other networks. Common IGPs are OSPF, ISIS or BGP. In my specific case, both Servers A & B run the Bird2 routing daemon with interior and exterior BGP sessions.

So how does the WireGuard HA setup interoperates with my interior routing? Quite well actually. As my notify script ( will automatically bring up/down the interface, the routes attached to the interface will be picked up by Bird’s direct protocol.

I am also planning to extend my WireGuard agent ɯice to support the synchronization of WireGuard interface configurations between multiple servers.


Surprisingly, the setup works by using Keepalived and does not require any iptables or nftables magic to rewrite source IP addresses. I’ve seen some people mentioning that SNAT/DNAT would be required to convince WireGuard to use the virtual IP instead of the server addresses. However, in my experience this was not necessary.

Another concern has been that the backup Wireguard interface still might attempt to establish a handshake with its peers. This would quite certainly interfere with the handshakes originated by the current master server. However, also this has not been proven to be the case. I assume the fact that our notify script brings down the WireGuard interface on the backup server causes them to cease all communication with its peers.

Gaining Root Access on Netgear Nighthawk Mobile 5G/LTE Routers

This blog posts covers the required steps to gain root access via Telnet on Netgear Nighthawk Mobile 5G/LTE Routers. Its the first post in a small series covering my experiences playing around with this device.

Last month I obtained one of Netgear’s latest mobile 5G routers, the Netgear Nighthawk M5 (model MR5200-100EUS) . Being one of the most expensive consumer 5G routers, I was lucky to get a fairly good second hand deal from eBay.

The router is powered by Qualcomm’s® Snapdragon X55 5G Modem-RF system. Looking closer at the internals of the device by checking the FCC filing for the closely related American model MR5100, we can see that the system consists of a Qualcomm SDX55 chipset which combines both the mobile baseband and application processors.

Gaining root access

Gaining root access to the device is actually fairly simple in comparison to rooting modern Android-based devices. The router exposes an open TCP port providing an AT command interface. However, this port is only accessible via a tethered USB connection, not via Wifi.

Using this AT command interface, we can interact with the modem, unlock an extended command set which allows us enable a Telnet daemon.

Detailed steps

1. Install the Sierra Wireless debug tools from bkerler:

sudo apt install python3 git
git clone
cd edl
sudo python install

(More detailed installation instructions are covered in the README file of the repo.)

2. Connect your machine via USB-C to the Netgear router.

3. Make sure to disconnect from the Netgear Wifi.

4. Open a terminal an connect to the AT command interface via netcat (nc).
(Make sure not to miss the -c option as it will the enable nc to use the proper CRLF line-endings which are required for the AT interface).

nc -c 5510

4. Once connected to the AT command interface, you need to request a unlock challenge code by sending:


The previous command will return a challenge code which we use to generate a corresponding response code via the previously installed tool: -l <replace_with_challenge_code> -d SDX55

The previous command will print out another AT+OPENLOCK command which you need to copy verbatim back to your AT command session.

5. Run the following AT commands to enable the Telnet daemon:


You can now close the AT command session by pressing Ctrl+C.

6. Power-cycle the Netgear Router to start the Telnet daemon.

Voila, you can now telnet into the device via both the tethered USB-C cable or Wifi.

nc -c 23
mdm 1623 sdxprairie
/ # uname -a
uname -a
Linux sdxprairie 4.14.117 #1 PREEMPT Thu Aug 19 23:42:26 UTC 2021 armv7l GNU/Linux

Disclaimer: Please be aware that the device security is now breached as all devices connected to the Wifi or USB can gain root access to the device. The root Telnet login requires no password.

Next steps

Before proceeding we should make sure that we can bring the device back to a secure state by replacing the Telnet by an Secure Shell (SSH) daemon. In one of the next posts of this series, I will be building a statically linked version of the Dropbear SSH server to replace Telnet.

Before continuing my reverse engineering efforts on the device, I would like to ensure that I will not brick the router while doing so by dumping the firmware and extract all the details from it. This will allow us to hopefully restore the device by flashing the original firmware. Maybe we will be able to run OpenWRT on it.

I have also designed a wall mount for the router which allows me to mount it permanently into by van.

Running a Xilinx hw_server as Docker Container

This article describes the necessary steps to run a Xilinx hw_server as a Docker container.

Xilinx’s hw_server is a command line utility which handles JTAG communication between a Xilinx FPGA board and usually the Vivado IDE. It can be used to configure the FPGA bitstream, connect to the embedded logic analyzer cores (ILA) or perform debugging of processor cores via GDB and the Xilinx System Debugger (XSDB). The hw_server is usually used when those tasks shall performed remotely as the connection between Vivado or XSDB is established via TCP connection and allows us to run it on a remote system.

Running the hw_server as a Docker container has the benefit that its installation is simplified to starting a Docker container by running:

docker run --restart unless-stopped --privileged --volume /dev/bus/usb:/dev/bus/usb --publish 3121:3121 --detach

It also allows us to run the hw_server on architectures which are not natively supported by Xilinx such as the commonly used Aarch / ARM64 and ARMv7 architectures found in Raspberry Pis.

This is enabled by Dockers support for running container images for non-native architectures. I am using the aptman/qus image to setup this user-mode emulation. qemu-user-static (qus) is a compilation of utilities, examples and references to build and execute OCI images (aka docker images) for foreign architectures using QEMU’s user-mode emulation.

Run the following commands to run the hw_server on a embedded device:

# Install docker
sudo apt-get update && sudo apt-get upgrade
curl -sSL | sh

# Start Docker
sudo systemctl enable --now docker

# Enable qemu-user emulation support for running amd64 Docker images
# *Note:* only required if your system arch is not amd64!
docker run --rm --privileged aptman/qus -s -- -p x86_64

# Run the hw_server
docker run --restart unless-stopped --privileged --volume /dev/bus/usb:/dev/bus/usb --publish 3121:3121 --detach

This setup has been tested with a Raspberry Pi 4 running the new 64-bit Debian Bullseye Raspberry Pi OS.

The pre-built Docker image for the hw_server of Vivado 2021.2 is available via

Detailed instructions can be found in the following Git repo:

Encrypted credentials for Amazon AWS command line client

In this quick post I will show howto use the password manager „password-store1 to securely store your credentials used by the Amazon Webservices command line client.

The installation for Mac and Linux system is fairly easy:
$ pip install awscli

The credentials are stored as key-value pairs inside a PGP-encrypted file.
Everytime you call the AWS CLI tool, your keys will be decrypted and directly passed to the aws tool.

Use pass to add your keys in the store:
$ pass edit providers/aws

An editor opens. Use the following format:
User: stv0g
Secret-Key: vAAABn/PMAksd235gAs/FSshhr42dg2D4EY3

Add the following snippet to your .bashrc:

function aws {
	local PASS=$(pass providers/aws)
	local AWS=$(which aws)

	# Start original aws executable with short-lived keys
	AWS_ACCESS_KEY_ID=$(sed -En 's/^Access-Key: (.*)/\1/p' <<< "$PASS") \
	AWS_SECRET_ACCESS_KEY=$(sed -En 's/^Secret-Key: (.*)/\1/p' <<< "$PASS") $AWS $@

Then use the cli tool aws as usual:
$ aws iam list-access-keys
{ "AccessKeyMetadata": [ { "UserName": "stv0g", ...

Use Yubikey and Password-store for Ansible credentials

I spent some time over the last months to improve the security of servers and passwords. In doing so, I started to orchestrate my servers using a configuration management tool called Ansible. This allows me to spin-up fresh servers in a few seconds and to get rid of year-old, polluted and insecure system images.


My ’single password for everything‘ has been replaced by a new password policy which enforces individual passwords for every single service. This was easier than I previously expected:

To unlock the ‚paranoid‘ level, I additionally purchased a Yubikey Neo token to handle the decryption of my login credentials in tamper-proof hardware.
pass‚ is just a small shell script to glue several existing Unix tools together: Bash, pwgen, Git, xclip & GnuPG (obeying the Unix philosophy). The passwords are stored in simple text files which are encrypted by PGP and stored in a directory structure which is managed in a Git repository.

Yubikey Neo und Neo-n

There are already a tons of tutorials which present the tools I describes above. I do not want to repeat all that stuff. So, this post is dedicated to solve some smaller issues I encountered:

Use One-Time passwords across multiple servers

The Yubikey Neo can do much more than decrypting static passwords via GnuPG:

  • Generate passwords:
    • fixed string (insecure!)
    • with Yubico OTP algorithm
    • with OATH-HOTP algorithm
  • Do challenge response authentication
    • via FIDO’s U2F standard
    • with HMAC-SHA1 algorithm
    • with Yubico OTP algorithm

Some third-party services already support FIDO U2F standard or traditional OATH-{H,T}OTP TFA, like used by the Google authenticator app. I suggest to have a look at:

For private servers there are several PAM modules available to integrate OTP’s or Challenge Response (CR) methods. Unfortunately, support for CR is not widespread across different SSH- and mail clients.

So, you want to use OTP’s which leds to another problem: OTP’s rely on a synchronized counter between the hardware token and the server. Once you use multiple servers, those must be synchronized as well. I’m using a central Radius server to facilitate this.

Integrate ‚pass‘ into your Ansible workflow

Ansible uses SSH and Python scripts to manage several remote machines in parallel. You must use key-based SSH authentication, because you do not want to type every password manually! Additionally you need to get super user privileges for most of your administrative tasks on the remote machine.

The SSH authentication is handled by gpg-agents ‚–enable-ssh-support‘ option and a PGP key on your token.

To get super user privileges, I use the following variable declaration my Ansible „group_vars/all“ file:
ansible_sudo_pass: "{{ lookup('pipe', 'pass servers/' + inventory_hostname) }}"

There is a separate root password for every server (e.g. „pass servers/“). I wrote some ansible roles to easily and periodically roll those passwords.

Integrate ‚pass‘ into OS X

There are already several plugins and extensions to intergrate the ‚pass‘ password store into other Programs like Firefox and Android.

A prompt for the password you want

I added support for OS X by writing a small AppleScript which can be found here:

A notification with countdown