The IEEE 802.1D standard, first published in 1990, formally defined transparent bridging as a method to connect network segments at the data link layer (Layer 2). The standard's language consistently uses the term "bridge" to describe devices that:

• Learn MAC addresses by examining source addresses in frames
• Forward frames based on destination MAC addresses
• Implement the spanning tree protocol to prevent loops

In the mid-1990s, vendors began marketing "switches" that fundamentally performed the same functions as bridges but with key implementation differences:

// Pseudocode showing bridge vs switch forwarding logic
// Traditional bridge (software-based)
void bridgeForward(Frame frame) {
    updateMacTable(frame.source, frame.inPort);
    if (macTable.contains(frame.destination)) {
        forward(frame, macTable[frame.destination]);
    } else {
        flood(frame); // Send to all ports except ingress
    }
}

// Modern switch (hardware-based)
void switchForward(Frame frame) {
    asic.learn(frame.source, frame.inPort); // Hardware MAC learning
    forwardingEngine.process(frame); // Dedicated forwarding chip
}

While many sources claim bridges typically have two ports, the 802.1D standard makes no such limitation. The confusion stems from:

The fundamental difference lies in performance optimization:

• Store-and-forward bridges: Complete frame validation (CRC check) before forwarding
• Cut-through switches: Begin forwarding after reading destination MAC (lower latency)
• Fragment-free switches: Hybrid approach checking first 64 bytes

Consider this Python simulation of forwarding behavior:

class NetworkDevice:
    def __init__(self, ports):
        self.mac_table = {}
        self.ports = ports
        
    def process_frame(self, frame, in_port):
        # Base implementation matches bridge behavior
        self.mac_table[frame.src_mac] = in_port
        if frame.dst_mac in self.mac_table:
            return [(frame, self.mac_table[frame.dst_mac])]
        else:
            # Flood to all ports except incoming
            return [(frame, p) for p in self.ports if p != in_port]

class Switch(NetworkDevice):
    def __init__(self, ports, hardware_accel=True):
        super().__init__(ports)
        self.hardware_accel = hardware_accel
        self.forwarding_rate = 1e9 if hardware_accel else 1e6  # Gbps vs Mbps
        
    def process_frame(self, frame, in_port):
        if self.hardware_accel:
            # Hardware-optimized path
            return super().process_frame(frame, in_port)[:1]  # Never floods
        else:
            return super().process_frame(frame, in_port)

Key observations from networking standards:

• IEEE 802.1D-2004 still uses "bridge" exclusively
• RFC 4363 (Layer 2 VPNs) uses both terms interchangeably
• Cisco documentation distinguishes based on port density

When choosing between bridge and switch terminology in documentation:

/* Recommended practice for network diagrams */
network_device {
    type: SWITCH, // Use for hardware-based multi-port devices
    function: BRIDGING, // Indicates standards-compliant behavior
    ports: 24,
    forwarding: HARDWARE_ACCELERATED
}

From a networking standards perspective, IEEE 802.1D defines a bridge as a device that connects multiple network segments at the data link layer (Layer 2). The standard makes no assumptions about port count or implementation method. Here's how the forwarding logic typically works in pseudocode:

function forwardFrame(frame, incomingPort) {
    // Learn source MAC address
    macTable[frame.sourceMac] = incomingPort;
    
    // Forwarding decision
    if (frame.destMac in macTable) {
        // Unicast to known port
        if (macTable[frame.destMac] != incomingPort) {
            forwardToPort(macTable[frame.destMac], frame);
        }
    } else {
        // Flood to all ports except incoming
        floodFrame(frame, incomingPort);
    }
}

The term "switch" emerged in the 1990s as vendors began marketing bridges with:

• Higher port densities (8+ ports)
• Hardware-based forwarding (ASICs instead of CPU)
• Non-blocking architectures

This Cisco configuration snippet shows how modern switches still use bridging concepts:

Switch# configure terminal
Switch(config)# bridge 1 protocol ieee
Switch(config)# interface FastEthernet0/1
Switch(config-if)# bridge-group 1

Key observations from IEEE 802.1D-2004:

1. Uses "bridge" terminology exclusively
2. Specifies behavior, not implementation
3. Covers both transparent bridging and source route bridging

Here's a Python simulation showing how both devices use the same core algorithm:

class NetworkDevice:
    def __init__(self):
        self.mac_table = {}
        
    def process_frame(self, frame, in_port):
        self.mac_table[frame.src_mac] = in_port
        if frame.dst_mac in self.mac_table:
            out_port = self.mac_table[frame.dst_mac]
            if out_port != in_port:
                self.forward(out_port, frame)
        else:
            self.flood(in_port, frame)

class Bridge(NetworkDevice):
    # Additional bridge-specific methods
    pass

class Switch(NetworkDevice):
    # Additional switch-specific optimizations
    def forward(self, port, frame):
        # Hardware-accelerated forwarding
        asic.forward(port, frame)

All switches are bridges (per IEEE standards), but not all bridges meet modern expectations for switches. The terminology difference primarily reflects marketing and implementation evolution rather than fundamental technical distinctions.