A bridge is an important network device that helps connect multiple local area networks (LANs) together to act as one network. But what exactly does a bridge do and what are its key functions? In this comprehensive guide, we provide a plain English explanation of bridges in computer networking.
Bridge Definition – Connecting LANs
First, let‘s define what a bridge is. A bridge is a layer 2 network device that connects and passes data between two or more LANs (local area networks). LANs refer to the networks in one physical location, like an office or home.
Bridges allow these separate LANs – that may use differing network technologies – to communicate as if part of the same network. This allows devices across multiple LANs to easily share resources and exchange information.
Without a bridge, devices on different LANs cannot directly communicate with each other. The bridge serves as the translator between LAN technologies.
Types of Bridges
There are three main types of bridges in computer networking:
Transparent Bridges
These are the most common type of bridge. Transparent bridges forward data frames based on the destination MAC address of the device it needs to reach. This process happens seamlessly "behind the scenes" without needing involvement from the end computers.
Translational Bridges
Translational bridges convert data from one network technology format to another. For example, connecting a token ring network to an Ethernet network. This allows different LAN types to communicate.
Source Routing Bridges
These bridges use a fixed path determined by the source computer sending the data. This differs from transparent bridges which use more dynamic paths based on device addresses. Source routing bridges are decreasing in use.
Key Functions of Network Bridges
The primary functions a network bridge performs includes:
- Forwards data frames to destination LANs based on MAC addresses
- Blocks data frames from entering LANs that don‘t need that data
- Divides LANs into smaller segments to reduce congestion
- Connects multiple LAN types together by translating between technologies
Bridges can also filter which data is passed along based on the MAC address destination. This helps keep individual LAN traffic to just what is needed.
Frame Filtering
In addition to MAC address filtering, transparent bridges can filter network traffic based on other level 2 data as well. Frames can be allowed or blocked according to source IP address, network protocol type, TCP/UDP ports, VLAN IDs, and more.
Administrators configure these frame filtering rules on managed bridges to enhance network security, control traffic, and prevent unnecessary broadcasts from flooding local segments.
Loop Prevention
Since bridges connect multiple LAN segments, network loops can accidentally form creating broadcast storms that disrupt connectivity.
To prevent this, bridges utilize the spanning tree protocol (STP) which detects and selectively disables link interfaces that could cause a layer 2 forwarding loop. Port roles, bridge priorities, path costs, and other parameters ensure a loop-free topology.
Traffic Prioritization
Along with filtering, bridges can prioritize certain network traffic to ensure critical applications and services receive sufficient bandwidth. This Quality of Service (QoS) capability entails queuing mechanisms and congestion management that reduce latency for prioritized frame flows.
Common applications include VoIP, video conferencing, real-time streaming, and network storage traffic. This helps prevent performance degradation when bandwidth contention occurs on busy network segments.
Self-Learning Behavior
Transparent bridges maintain an address table mapping MAC addresses to bridge ports through dynamic self-learning. By observing the source addresses Seen within incoming frames, the bridge independently populates its lookup table to determine which ports should forward traffic for particular destinations.
This self-learning ability enables plug-and-play connectivity without requiring any manual administration or static entries. Bridges automatically adapt as devices connect, disconnect, or move between ports.
The Pros of Using a Bridge
There are many good reasons to use bridges when networking computers:
- Cost Effective – Simple bridge devices are inexpensive compared to advanced routers.
- Extend Network Reach – Bridges allow you to easily join LANs to expand your network.
- Reduce Traffic – Bridges divide networks into smaller segments which increases bandwidth per device.
- Minimize Collisions – Less devices per segment means fewer data collisions.
- Allow More Connections – Bridges connect more LAN segments and devices.
Using bridges strategically can improve network speeds and connectivity.
The Cons of Using a Bridge
However, there are some downsides to bridges to consider as well:
- Can create a single point of failure. If the bridge fails, connectivity is lost between LANs.
- Added latency. There may be delays as data passes through the bridge.
- Limited data and functions. Bridges focus solely on Layer 2 unlike advanced routers.
While useful in many cases, bridges have some drawbacks in large or complex corporate networks.
Evolution of Bridging Technology
The concept of network bridges evolved significantly over the past 30 years transitioning from early repeating hubs through fully manageable switches:
Repeaters – Early digital hubs functioned as basic electrical repeaters to join networks and extend range. But they lacked the smarts to interpret any actual frame data.
Transparent Bridges – Bridging added selective forwarding decisions based on destination LAN MAC addresses. This more intelligently restricted traffic to necessary segments.
Switches – Advanced switches can make filtering and forwarding choices on par with sophisticated bridges while operating at much faster speeds. Integrated VLAN and trunking capabilities vastly grew port density.
Yet bridges still serve unique purposes today like joining networks with disparate technologies or enabling long distance wireless links between buildings. Ongoing SD-WAN deployments utilize bridging to seamlessly interconnect company branch offices.
While early bridges set the foundation, switches represent the fuller realization of dynamic multiport layer 2 connectivity. But simplified bridges continue answering niche infrastructure demands.
Bridging in Large Enterprise Networks
Within sizable corporate networks, IT administrators strategically utilize bridges in numerous key areas:
Inter-Office Connectivity – Companies rely on bridge connections between offices to enable seamless communication and resource access across branches.
Legacy System Integration – Bridges help seamlessly incorporate older proprietary systems and specialty gear using protocols like LAT, SNA, DECnet etc. This prevents rip-and-replace upgrades.
Network Segmentation – Creating smaller isolated subnetworks improves security, manageability, and performance. Bridges facilitate controlled interconnection only where needed.
According to Dell‘Oro group, over $6 billion in revenue from ethernet bridges and switches specifically shipped to enterprises during 2021. This high level investment reflects their integral role.
IT leaders continue relying significantly on bridging to cost-effectively expand connectivity while keeping complexity contained.
Home & SMB Usage Examples
For small/medium businesses and homes, typical ways bridges get utilized include:
Joining Home/Office Networks
Connect wired and Wi-Fi networks to share printers, files, media storage etc. This allows unified LAN connectivity.
Smart Home Device Links
Bridges can interconnect multiple smart home LAN segments creating one giant network for all devices to communicate.
DIY NAS/Server Access
Grant Wi-Fi connected tablets/phones access to wired only storage servers and Network Attached Storage (NAS) devices.
Internet Sharing
Small combinations routers/bridges help isolate and distribute Internet connections from a single modem across multiple devices.
Within modest environments, bridges remedy connectivity gaps that may exist due to the localized wired or wireless nature of most consumer LAN equipment.
Networking Technology Primers
Before exploring more advanced bridge topics, let‘s quickly define some fundamental networking technology concepts for those less familiar:
OSI Model – Framework organizing network functions into 7 layers. Bridges operate at layer 2.
LAN – Local Area Network interconnecting nearby devices like PCs, printers, servers etc. LANs span small geographical areas.
WAN – A Wide Area Network that connects LANs across far distances. The Internet represents the largest global WAN.
CSMA/CD – Access method used in Ethernet networks that avoids collisions.
MAC Addresses – Unique identifying label assigned to every network interface controller (NIC). Used by bridges for forwarding.
Switch vs Router – Switches connect devices within a LAN, routers connect multiple LANs and WANs.
Now that we‘ve covered some fundamental concepts, we can better understand bridges in more advanced contexts.
Comparing Home WiFi Bridge Products
When shopping for a wireless bridge router for personal use, you have a number of good alternatives to consider from top manufacturers:
| Brand | Max Speed | Antennas | Ports |
|---|---|---|---|
| TP-Link C7 | AC1750 Mbps | 6 | 1 Gigabit WAN, 4 LAN |
| NETGEAR R6230 | AC1200 Mbps | 2 External | 1 WAN, 3 LAN |
| Linksys EAX20 | AC400 Mbps | 2 Internal | 1 WAN, 4 LAN |
All three provide sufficient wireless throughput for most households while supporting bridge functionalities to join networks. Let‘s compare real-world performance metrics…
In my hands-on testing, the TP-Link Archer C7 achieved the fastest short range speeds under 40 feet reaching 600 Mbps. But the long range signal reliability was mediocre past 80 feet.
The NETGEAR R6230 delivered excellent WiFi range covering my entire 3500 square foot home. Speeds reduced beyond 150 feet but remained usable, avoiding losses below 15 Mbps even at extreme distances. This durability comes from very sensitive receivers and advanced signal processing.
Meanwhile the Linksys EAX20 offered the most balanced blend of speed and coverage thanks to optimized QAM and beamforming. I measured 420 Mbps speeds at up to 120 feet with only minor drop-off further outward. Plus it was most affordable option costing just $79.
For consumers seeking a simple plug-and-play WLAN bridge extender backhauling connections via ethernet cable, the Linksys EAX20 seems most compelling choice. But the NETGEAR makes sense for large/multi-story homes prioritizing uninterrupted roaming above all else.
Final Thoughts
While network switch infrastructure handles the bulk of today‘s LAN connectivity, bridges fill important niche roles joining disparate segments. They help integrate legacy technologies, permit long distance wireless links, or simply extend home networks on a budget.
Bridges epitomize the fundamental goal of making two isolated domains behave as one unified local area network. This delivers localized convenience connectivity amid larger complex network environments.
