Bridgepassthrough

Bridgepassthrough refers to a networking configuration in which a network bridge forwards traffic between its connected interfaces with little or no modification, effectively allowing devices on either side to communicate as if the bridge were not present. It operates primarily at layer 2, handling MAC addresses and frame forwarding rather than performing IP routing or network address translation.

A bridge in passthrough mode learns which MAC addresses are reachable on each connected segment and forwards frames accordingly. If the destination is unknown, the frame is flooded to all other ports. When configured to be VLAN-aware, the bridge can pass through frames with VLAN tags intact, preserving network segmentation across the bridged links.

Common use cases include virtualization environments and home or office networks. In virtualization, a bridge passthrough setup connects virtual machines to the physical network through a host bridge, providing direct L2 connectivity without intervening routing by the host. In consumer networks, a bridge or IP passthrough mode on a gateway or modem can hand over control of routing and NAT to an upstream or downstream device, effectively placing the gateway in a transparent bridge mode.

Benefits of bridgepassthrough include transparency to connected devices, preservation of VLAN tags, and minimal changes to device configurations. It is also useful for simplifying network designs where devices require direct access to the broader LAN or WAN.

Considerations include potential security risks, since traffic is not filtered or translated by the bridge itself. Proper access controls, VLAN configuration, and monitoring are important. Performance is typically modestly affected by the bridge’s processing, though modern bridges usually impose minimal overhead. Some vendors label similar setups as bridge mode, transparent bridging, or IP passthrough, depending on the context.