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Working with User Networking

BlackDog to host PC communications operate in a network environment that uses Network Address Translation (NAT). The NAT software resides on the host. The BlackDog is considered the NAT client, while the host PC is the NAT server. The NAT networking environment has the following features.

Address Translation. The NAT feature translates an Internet Protocol (IP) address used within an internal network to a different (usually global) IP address used in an external network. NAT translates all external requests originating from the BlackDog into the host PC's IP address before they are forwarded to an external network. Thus, BlackDog communications assume the address of the host PC for security purposes.

Disabled Inbound Host Connections. Inbound connections from external networks to the BlackDog are disabled as a security design feature of NAT. The host establishes connections to external networks on behalf of the BlackDog. If the NAT lookup table located on the host does not have an outgoing BlackDog reference for an incoming request, it will discard the incoming connection request. This prevents any malware located on external networks from migrating to the BlackDog and prevents attackers on external networks from accessing the device.

Note: You should only open connections from the BlackDog out to external networks, never in the opposite direction. The only exception is the direct connection from the PC host to the BlackDog.

Connection Availability. The NAT connection is up whenever a default route is available. The NAT network environment uses TCP, IP and IGMP (Internet Group Management Protocol). NAT does not work with ICMP (Internet Communication Message Protocol), which is used to PING devices.

Using Realm-networking (Linux). Realm-networking automatically runs on Windows operating systems. However, to connect the BlackDog to a Linux host PC's network, you (or your applications) must run Realm-networking manually. The SDK includes the source code you can compile to produce the binary in the SDK_HOME/src/user_nat directory. For more information, please refer to:

• Enabling BlackDog Networking on Linux under the Host-Specific Configuration Notes topic
• Realm-networking (user_nat) Reference Application (includes instructions for setting up the build environment required to build the SDK-supplied user_nat)

Starting User Networking. To start user mode networking on your Linux PC, run the following command:

Realm-networking 169.254.0.1

This allows your BlackDog to connect to networking available on your host PC.

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