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Supported platforms

Vyatta documentation

Learn how to install, configure, and operate the Vyatta Network Operating System (Vyatta NOS) and Orchestrator, which help drive our virtual networking and physical platforms portfolio.

Broadcast network (site-to-site, client, server)

By default, an OpenVPN interface is configured as a “tun” device. A tun device is a virtual network interface that operates on Layer 3 (network layer) traffic, such as IP packets. There are cases in which the virtual interface needs to operate on Layer 2 (link layer) traffic. One example of this need is when subnets on each end of a tunnel must reside on the same subnet. In this case, the two subnets must be bridged across the tunnel. Bridging occurs on Layer 2. Another example is when a DHCP Relay resides on one side of a tunnel and the DHCP Server or DHCP clients reside on the other side. Clients must broadcast DHCP discovery messages and require a broadcast network to broadcast these messages. Because of this necessity, DHCP Relay requires that all interfaces to which it binds are broadcast interfaces.

A “tap” device is a virtual network interface that operates on Layer 2 (link layer) traffic and provides a broadcast network. A tap device is automatically configured by the system if the OpenVPN tunnel is to be used to bridge two subnets. If an OpenVPN tunnel is added to a bridge group then a tap device is implied and does not need to be configured explicitly. For cases that do not involve bridging, a tap device must be configured explicitly by using the interfaces openvpn vtunx device-type tap command.