- Use alternative DNS servers
- Run without privileged mode
- Select VPN modes
- Access other containers on the Docker host
- Specify VPN server's public IP
- Assign static IPs to VPN clients
- Customize VPN subnets
- About host network mode
- Enable Libreswan logs
- Check server status
- Build from source code
- Bash shell inside container
- Bind mount the env file
- Deploy Google BBR congestion control
By default, clients are set to use Google Public DNS when the VPN is active. If another DNS provider is preferred, define VPN_DNS_SRV1 and optionally VPN_DNS_SRV2 in your env file, then follow instructions to re-create the Docker container. Example:
VPN_DNS_SRV1=1.1.1.1
VPN_DNS_SRV2=1.0.0.1
Use VPN_DNS_SRV1 to specify the primary DNS server, and VPN_DNS_SRV2 to specify the secondary DNS server (optional).
Note that if IKEv2 is already set up in the Docker container, you will also need to edit /etc/ipsec.d/ikev2.conf inside the Docker container and replace 8.8.8.8 and 8.8.4.4 with your alternative DNS server(s), then restart the Docker container.
Below is a list of some popular public DNS providers for your reference.
| Provider | Primary DNS | Secondary DNS | Notes |
|---|---|---|---|
| Google Public DNS | 8.8.8.8 | 8.8.4.4 | Default in this project |
| Cloudflare | 1.1.1.1 | 1.0.0.1 | See also: Cloudflare for families |
| Quad9 | 9.9.9.9 | 149.112.112.112 | Blocks malicious domains |
| OpenDNS | 208.67.222.222 | 208.67.220.220 | Blocks phishing domains, configurable. |
| CleanBrowsing | 185.228.168.9 | 185.228.169.9 | Domain filters available |
| NextDNS | Varies | Varies | Ad blocking, free tier available. Learn more. |
| Control D | Varies | Varies | Ad blocking, configurable. Learn more. |
Advanced users can create a Docker container from this image without using privileged mode (replace ./vpn.env in the command below with your own env file).
Note: If your Docker host runs CentOS Stream, Oracle Linux 8+, Rocky Linux or AlmaLinux, it is recommended to use privileged mode. If you want to run without privileged mode, you must run modprobe ip_tables before creating the Docker container and also on boot.
docker run \
--name ipsec-vpn-server \
--env-file ./vpn.env \
--restart=always \
-v ikev2-vpn-data:/etc/ipsec.d \
-p 500:500/udp \
-p 4500:4500/udp \
-d --cap-add=NET_ADMIN \
--device=/dev/ppp \
--sysctl net.ipv4.ip_forward=1 \
--sysctl net.ipv4.conf.all.accept_redirects=0 \
--sysctl net.ipv4.conf.all.send_redirects=0 \
--sysctl net.ipv4.conf.all.rp_filter=0 \
--sysctl net.ipv4.conf.default.accept_redirects=0 \
--sysctl net.ipv4.conf.default.send_redirects=0 \
--sysctl net.ipv4.conf.default.rp_filter=0 \
--sysctl net.ipv4.conf.eth0.send_redirects=0 \
--sysctl net.ipv4.conf.eth0.rp_filter=0 \
hwdsl2/ipsec-vpn-server
When running without privileged mode, the container is unable to change sysctl settings. This could affect certain features of this image. A known issue is that the Android/Linux MTU/MSS fix also requires adding --sysctl net.ipv4.ip_no_pmtu_disc=1 to the docker run command. If you encounter any issues, try re-creating the container using privileged mode.
After creating the Docker container, see Retrieve VPN login details.
Similarly, if using Docker compose, you may replace privileged: true in docker-compose.yml with:
cap_add:
- NET_ADMIN
devices:
- "/dev/ppp:/dev/ppp"
sysctls:
- net.ipv4.ip_forward=1
- net.ipv4.conf.all.accept_redirects=0
- net.ipv4.conf.all.send_redirects=0
- net.ipv4.conf.all.rp_filter=0
- net.ipv4.conf.default.accept_redirects=0
- net.ipv4.conf.default.send_redirects=0
- net.ipv4.conf.default.rp_filter=0
- net.ipv4.conf.eth0.send_redirects=0
- net.ipv4.conf.eth0.rp_filter=0
For more information, see compose file reference.
Using this Docker image, the IPsec/L2TP and IPsec/XAuth ("Cisco IPsec") modes are enabled by default. In addition, IKEv2 mode will be enabled if the -v ikev2-vpn-data:/etc/ipsec.d option is specified in the docker run command when creating the Docker container.
Advanced users can selectively disable VPN modes by setting the following variable(s) in the env file, then re-create the Docker container.
Disable IPsec/L2TP mode: VPN_DISABLE_IPSEC_L2TP=yes
Disable IPsec/XAuth ("Cisco IPsec") mode: VPN_DISABLE_IPSEC_XAUTH=yes
Disable both IPsec/L2TP and IPsec/XAuth modes: VPN_IKEV2_ONLY=yes
After connecting to the VPN, VPN clients can generally access services running in other containers on the same Docker host, without additional configuration.
For example, if the IPsec VPN server container has IP 172.17.0.2, and an Nginx container with IP 172.17.0.3 is running on the same Docker host, VPN clients can use IP 172.17.0.3 to access services on the Nginx container. To find out which IP is assigned to a container, run docker inspect <container name>.
On Docker hosts with multiple public IP addresses, advanced users can specify a public IP for the VPN server using variable VPN_PUBLIC_IP in the env file, then re-create the Docker container. For example, if the Docker host has IPs 192.0.2.1 and 192.0.2.2, and you want the VPN server to use 192.0.2.2:
VPN_PUBLIC_IP=192.0.2.2
Note that this variable has no effect for IKEv2 mode, if IKEv2 is already set up in the Docker container. In this case, you may remove IKEv2 and set it up again using custom options. Refer to Configure and use IKEv2 VPN.
Additional configuration may be required if you want VPN clients to use the specified public IP as their "outgoing IP" when the VPN connection is active, and the specified IP is NOT the main IP (or default route) on the Docker host. In this case, you can try adding an IPTables SNAT rule on the Docker host. To persist after reboot, you may add the command to /etc/rc.local.
Continuing with the example above, if the Docker container has internal IP 172.17.0.2 (check using docker inspect ipsec-vpn-server), Docker's network interface name is docker0 (check using iptables -nvL -t nat), and you want the "outgoing IP" to be 192.0.2.2:
iptables -t nat -I POSTROUTING -s 172.17.0.2 ! -o docker0 -j SNAT --to 192.0.2.2
To check the "outgoing IP" for a connected VPN client, you may open a browser on the client and look up the IP address on Google.
When connecting using IPsec/L2TP mode, the VPN server (Docker container) has internal IP 192.168.42.1 within the VPN subnet 192.168.42.0/24. Clients are assigned internal IPs from 192.168.42.10 to 192.168.42.250. To check which IP is assigned to a client, view the connection status on the VPN client.
When connecting using IPsec/XAuth ("Cisco IPsec") or IKEv2 mode, the VPN server (Docker container) does NOT have an internal IP within the VPN subnet 192.168.43.0/24. Clients are assigned internal IPs from 192.168.43.10 to 192.168.43.250.
Advanced users may optionally assign static IPs to VPN clients. IKEv2 mode does NOT support this feature. To assign static IPs, declare the VPN_ADDL_IP_ADDRS variable in your env file, then re-create the Docker container. Example:
VPN_ADDL_USERS=user1 user2 user3 user4 user5
VPN_ADDL_PASSWORDS=pass1 pass2 pass3 pass4 pass5
VPN_ADDL_IP_ADDRS=* * 192.168.42.2 192.168.43.2
In this example, we assign static IP 192.168.42.2 for user3 for IPsec/L2TP mode, and assign static IP 192.168.43.2 for user4 for IPsec/XAuth ("Cisco IPsec") mode. Internal IPs for user1, user2 and user5 will be auto-assigned. The internal IP for user3 for IPsec/XAuth mode and the internal IP for user4 for IPsec/L2TP mode will also be auto-assigned. You may use * to specify auto-assigned IPs, or put those user(s) at the end of the list.
Static IPs that you specify for IPsec/L2TP mode must be within the range from 192.168.42.2 to 192.168.42.9. Static IPs that you specify for IPsec/XAuth ("Cisco IPsec") mode must be within the range from 192.168.43.2 to 192.168.43.9.
If you need to assign more static IPs, you must shrink the pool of auto-assigned IP addresses. Example:
VPN_L2TP_POOL=192.168.42.100-192.168.42.250
VPN_XAUTH_POOL=192.168.43.100-192.168.43.250
This will allow you to assign static IPs within the range from 192.168.42.2 to 192.168.42.99 for IPsec/L2TP mode, and within the range from 192.168.43.2 to 192.168.43.99 for IPsec/XAuth ("Cisco IPsec") mode.
Note that if you specify VPN_XAUTH_POOL in the env file, and IKEv2 is already set up in the Docker container, you must manually edit /etc/ipsec.d/ikev2.conf inside the container and replace rightaddresspool=192.168.43.10-192.168.43.250 with the same value as VPN_XAUTH_POOL, before re-creating the Docker container. Otherwise, IKEv2 may stop working.
Note: In your env file, DO NOT put "" or '' around values, or add space around =. DO NOT use these special characters within values: \ " '.
By default, IPsec/L2TP VPN clients will use internal VPN subnet 192.168.42.0/24, while IPsec/XAuth ("Cisco IPsec") and IKEv2 VPN clients will use internal VPN subnet 192.168.43.0/24. For more details, read the previous section.
For most use cases, it is NOT necessary and NOT recommended to customize these subnets. If your use case requires it, however, you may specify custom subnet(s) in your env file, then you must re-create the Docker container.
# Example: Specify custom VPN subnet for IPsec/L2TP mode
# Note: All three variables must be specified.
VPN_L2TP_NET=10.1.0.0/16
VPN_L2TP_LOCAL=10.1.0.1
VPN_L2TP_POOL=10.1.0.10-10.1.254.254
# Example: Specify custom VPN subnet for IPsec/XAuth and IKEv2 modes
# Note: Both variables must be specified.
VPN_XAUTH_NET=10.2.0.0/16
VPN_XAUTH_POOL=10.2.0.10-10.2.254.254
Note: In your env file, DO NOT put "" or '' around values, or add space around =.
In the examples above, VPN_L2TP_LOCAL is the VPN server's internal IP for IPsec/L2TP mode. VPN_L2TP_POOL and VPN_XAUTH_POOL are the pools of auto-assigned IP addresses for VPN clients.
Note that if you specify VPN_XAUTH_POOL in the env file, and IKEv2 is already set up in the Docker container, you must manually edit /etc/ipsec.d/ikev2.conf inside the container and replace rightaddresspool=192.168.43.10-192.168.43.250 with the same value as VPN_XAUTH_POOL, before re-creating the Docker container. Otherwise, IKEv2 may stop working.
Advanced users can run this image in host network mode, by adding --network=host to the docker run command. In addition, if running without privileged mode, you may also need to replace eth0 with the network interface name of your Docker host.
Host network mode is NOT recommended for this image, unless your use case requires it. In this mode, the container's network stack is not isolated from the Docker host, and VPN clients may be able to access ports or services on the Docker host using its internal VPN IP 192.168.42.1 after connecting using IPsec/L2TP mode. Note that you will need to manually clean up the changes to IPTables rules and sysctl settings by run.sh or reboot the server when you no longer use this image.
Some Docker host OS, such as Debian 10, cannot run this image in host network mode due to the use of nftables.
To keep the Docker image small, Libreswan (IPsec) logs are not enabled by default. If you need to enable it for troubleshooting purposes, first start a Bash session in the running container:
docker exec -it ipsec-vpn-server env TERM=xterm bash -l
Then run the following commands:
# For Alpine-based image
apk add --no-cache rsyslog
rsyslogd
rc-service ipsec stop; rc-service -D ipsec start >/dev/null 2>&1
sed -i '/pluto\.pid/a rsyslogd' /opt/src/run.sh
exit
# For Debian-based image
apt-get update && apt-get -y install rsyslog
rsyslogd
service ipsec restart
sed -i '/pluto\.pid/a rsyslogd' /opt/src/run.sh
exit
Note: The error rsyslogd: imklog: cannot open kernel log is normal if you use this Docker image without privileged mode.
When finished, you may check Libreswan logs with:
docker exec -it ipsec-vpn-server grep pluto /var/log/auth.log
To check xl2tpd logs, run docker logs ipsec-vpn-server.
Check the status of the IPsec VPN server:
docker exec -it ipsec-vpn-server ipsec status
Show currently established VPN connections:
docker exec -it ipsec-vpn-server ipsec trafficstatus
Advanced users can download and compile the source code from GitHub:
git clone https://github.com/hwdsl2/docker-ipsec-vpn-server
cd docker-ipsec-vpn-server
# To build Alpine-based image
docker build -t hwdsl2/ipsec-vpn-server .
# To build Debian-based image
docker build -f Dockerfile.debian -t hwdsl2/ipsec-vpn-server:debian .
Or use this if not modifying the source code:
# To build Alpine-based image
docker build -t hwdsl2/ipsec-vpn-server github.com/hwdsl2/docker-ipsec-vpn-server
# To build Debian-based image
docker build -f Dockerfile.debian -t hwdsl2/ipsec-vpn-server:debian \
github.com/hwdsl2/docker-ipsec-vpn-server
To start a Bash session in the running container:
docker exec -it ipsec-vpn-server env TERM=xterm bash -l
(Optional) Install the nano editor:
# For Alpine-based image
apk add --no-cache nano
# For Debian-based image
apt-get update && apt-get -y install nano
Then run your commands inside the container. When finished, exit the container and restart if needed:
exit
docker restart ipsec-vpn-server
As an alternative to the --env-file option, advanced users can bind mount the env file. The advantage of this method is that after updating the env file, you can restart the Docker container to take effect instead of re-creating it. To use this method, you must first edit your env file and use single quotes '' to enclose the values of all variables. Then (re-)create the Docker container (replace the first vpn.env with your own env file):
docker run \
--name ipsec-vpn-server \
--restart=always \
-v "$(pwd)/vpn.env:/opt/src/env/vpn.env:ro" \
-v ikev2-vpn-data:/etc/ipsec.d \
-v /lib/modules:/lib/modules:ro \
-p 500:500/udp \
-p 4500:4500/udp \
-d --privileged \
hwdsl2/ipsec-vpn-server
After the VPN server is set up, the performance can be improved by deploying the Google BBR congestion control algorithm on your Docker host.
This is usually done by modifying the configuration file /etc/sysctl.conf. However, some Linux distributions may additionally require updates to the Linux kernel.
For detailed deployment methods, please refer to this document. When finished, restart the Docker container:
docker restart ipsec-vpn-server
Note: The software components inside the pre-built image (such as Libreswan and xl2tpd) are under the respective licenses chosen by their respective copyright holders. As for any pre-built image usage, it is the image user's responsibility to ensure that any use of this image complies with any relevant licenses for all software contained within.
Copyright (C) 2016-2023 Lin Song
This work is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License
Attribution required: please include my name in any derivative and let me know how you have improved it!
