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Bridging and Forwarding Techniques in Linux Networking

Protocol bridges are software or hardware components that connect different network protocols or transports, enabling seamless data transfer between incompatible communication methods.

1. Introduction

Network bridges come in two main categories:

  1. Layer 2 bridges, which operate at the Data Link layer to connect Ethernet segments by forwarding frames based on MAC addresses — essentially making multiple physical or virtual networks act as one LAN.

  2. Protocol bridges, which operate at higher layers (Layer 4 and above) and connect different network protocols or transports — for example, converting UDP to TCP or bridging serial ports to network sockets.

In this section, we focus on protocol bridges and their diverse use cases in modern networking.

My Note:

  • Layer 2 bridging is a formal and standard concept in networking.

  • Protocol bridging is a common, practical term to describe bridging beyond Layer 2, but not an official standard category.

2. List of tools and techniques

Below is a list of common network and protocol bridging tools and techniques, along with typical use cases and whether they support bidirectional communication.

Bridge Type Description Example Use Case Bidirectional?
UDP → TCP Bridge Converts UDP packets to TCP streams and vice versa Forward UDP sensor data reliably over TCP No (usually)
TCP → TCP Bridge (Proxy) Forwards TCP connections from one port to another Simple TCP proxy or port forwarder Yes
Serial Port → TCP Bridge Bridges serial devices (e.g., /dev/ttyS0) to TCP Remote access to serial devices over network Yes
UNIX Socket → TCP Bridge Bridges local UNIX domain socket to TCP socket Container socket forwarding or local IPC Yes
IPv4 → IPv6 Bridge Converts IPv4 connections to IPv6 and vice versa Legacy-IPv4 to modern IPv6 service access Yes
TCP → SSL/TLS Bridge Adds SSL/TLS encryption to plain TCP connections Secure legacy TCP connections Yes
Raw Socket → TCP/UDP Bridge Bridges raw network packets to TCP/UDP sockets Specialized packet forwarding or monitoring Yes
PTY (Pseudo-terminal) Bridge Connects pseudo terminals for virtual serial ports Emulates serial ports for applications Yes
File → Network Bridge Sends file contents over a network socket File transfer via TCP/UDP No
Network → File Bridge Receives network data and saves to a file Packet capture or logging No
Multicast → Unicast Bridge Converts multicast streams to unicast Deliver multicast streams over unicast networks No
TCP Load Balancer (Round Robin) Distributes TCP connections across backend servers Basic load balancing for TCP services Yes
Port Knocking Handler Listens on ports and triggers scripts Firewall port opening based on knock sequences No
Virtual Network Interface Bridge Bridges virtual interfaces (e.g., tap, tun) VPN tunnels and container networking Yes
UDP Multicast Forwarder Forwards multicast UDP packets to multiple endpoints Streaming media or device discovery No

3. Additional resources on this website

This site covers many of the topics listed above in greater detail. Feel free to explore more!
For your convenience, relevant links and references are provided at the end of this page.

Data Pipelining