Docker Network Traffic with Cisco VPN Connection: Bridging Access for Containers on Company LAN

Bridging Docker Network Traffic with Cisco VPN Connection: Accessing Company LAN for Containers

In today's interconnected world, businesses rely heavily on virtual private networks (VPNs) to securely access their company's local area network (LAN) from remote locations. Docker, a popular containerization platform, also requires network connectivity to access the host system and other containers. This article will explore the concept of bridging Docker network traffic with a Cisco VPN connection, allowing containers to access devices on the company's LAN.

Understanding the Basics

To begin with, it is essential to understand the basic components involved in this setup:

• Docker: An open-source platform that automates the deployment, scaling, and management of applications using containers.
• Cisco AnyConnect VPN: A secure VPN client developed by Cisco Systems, providing remote access to enterprise networks.
• Company LAN: The internal network of a company, which typically includes various devices such as servers, workstations, and network-attached storage (NAS) devices.
• Bridging: The process of connecting two networks, enabling communication between them.

The Challenge: Routing Docker Traffic through Cisco AnyConnect VPN

By default, Docker containers use the host system's network interfaces for communication. When a Cisco AnyConnect VPN connection is established, all network traffic is routed through the VPN tunnel, including Docker container traffic. This can be problematic, as it may prevent containers from accessing devices on the company's LAN directly.

To overcome this challenge, we can create a bridge between the Docker network and the Cisco AnyConnect VPN interface, allowing containers to access devices on the company's LAN as if they were directly connected to the same network.

Setting Up the Bridge

To set up the bridge, follow these steps:

1. Identify the name of the Cisco AnyConnect VPN interface. This is typically cscotun0 but can vary depending on the system configuration.
2. Create a new Docker network using the --subnet and --gateway options to specify the IP address range and default gateway for the network. For example:

   docker network create --driver=bridge --subnet=10.0.0.0/24 --gateway=10.0.0.1 my-bridge-network
   

3. Connect the Docker containers to the newly created network.
4. Configure the bridge between the Docker network and the Cisco AnyConnect VPN interface. This can be done using the ip command, as shown below:

   sudo ip link add name docker-vpn type bridge
   sudo ip link set docker-vpn up
   sudo ip link set cscotun0 master docker-vpn
   sudo ip link set cscotun0 up
   sudo ip addr add 10.0.0.2/24 dev docker-vpn
   

   This configuration creates a new bridge interface called docker-vpn, attaches the Cisco AnyConnect VPN interface (cscotun0) to it, and assigns an IP address within the Docker network's subnet (10.0.0.2/24).

Testing the Setup

To test the setup, start a container connected to the new Docker network and attempt to access a device on the company's LAN. For example:

docker run -it --rm --network my-bridge-network alpine ping 10.0.0.1

If the setup is correct, the container should be able to reach the device on the company's LAN.

Bridging Docker network traffic with a Cisco VPN connection allows containers to access devices on the company's LAN, overcoming the limitations imposed by the VPN tunnel. By creating a bridge between the Docker network and the Cisco AnyConnect VPN interface, containers can communicate with LAN devices as if they were directly connected to the same network.

References

• Docker network create
• Cisco AnyConnect Administr