When both ends of an Ethernet patch cable are connected to the same hub or switch, it creates a Layer 2 loop in your network. This forms a broadcast storm where packets endlessly circulate through the loop, exponentially increasing network traffic until the bandwidth is completely saturated.

Here's what happens at the protocol level:

1. A broadcast packet enters the loop
2. The hub (being a dumb device) forwards it to all ports
3. The packet returns through the looped cable
4. The process repeats indefinitely

Unlike switches that use spanning tree protocol (STP), most basic hubs lack loop prevention mechanisms. This causes:

• ARP table corruption
• MAC address flapping
• TCP retransmission storms

You can identify loops using these technical approaches:

// Python example using scapy to detect broadcast storms
from scapy.all import *

def packet_callback(pkt):
    if pkt[Ether].dst == "ff:ff:ff:ff:ff:ff":
        print(f"Broadcast storm detected from {pkt[Ether].src}")

sniff(prn=packet_callback, store=0)

For network administrators, key indicators include:

show interface counters | include broadcast
show mac address-table count | include flapping

Enterprise solutions include:

1. Implementing STP/RSTP on all switches
2. Using loop guard and BPDU protection
3. Physical port security with MAC binding

For smaller networks, consider:

# Simple bash script to monitor port status
while true; do
    netstat -i | grep -i "collision"
    sleep 5
done

A 2019 case study showed how a single looped cable in a financial institution:

• Reduced network throughput by 87%
• Caused 14 switches to crash
• Resulted in 32 minutes of trading downtime

The economic impact was estimated at $240,000 per minute during peak hours.

For modern DevOps environments:

# Prometheus alert rule for broadcast storms
- alert: NetworkLoopDetected
  expr: rate(node_network_receive_bytes_total{device=~"eth.*"}[1m]) > 100000000
  for: 2m
  labels:
    severity: critical
  annotations:
    summary: "Network loop detected on {{ $labels.instance }}"

---

During routine network troubleshooting using a nested-interval approach, we identified a 4-port hub with a loopback configuration where both ends of a Cat5e patch cable were connected to the same device. This created a classic Layer 2 broadcast storm scenario, though interestingly without triggering error LEDs on either the hub or upstream switch.

When you short-circuit a network segment by creating a loop:

1. ARP and DHCP packets begin circulating indefinitely
2. The switch's MAC address table becomes unstable
3. Bandwidth gets consumed by redundant frame propagation

The absence of physical damage occurs because Ethernet interfaces have current-limiting protection, but the logical network impact can be severe.

Here's what Wireshark would show during such an event:

No.     Time        Source           Destination      Protocol Length Info
1 0.000000   Broadcast         Broadcast         ARP      42     Who has 192.168.1.1? Tell 192.168.1.2
2 0.000012   Broadcast         Broadcast         ARP      42     Who has 192.168.1.1? Tell 192.168.1.2 
3 0.000023   Broadcast         Broadcast         ARP      42     Who has 192.168.1.1? Tell 192.168.1.2
[...repeating thousands of times...]

Modern networks implement safeguards:

• Spanning Tree Protocol (STP): Enabled by default on managed switches
• BPDU Guard: Blocks unauthorized bridge connections
• Loop Protection: Found in protocols like Ethernet Ring Protection (ERP)

For Python network automation scripts, you could check for loops programmatically:

import scapy.all as scapy

def detect_broadcast_storm(pcap_file, threshold=1000):
    packets = scapy.rdpcap(pcap_file)
    arp_count = sum(1 for p in packets if p.haslayer(scapy.ARP))
    return arp_count > threshold

The physical layer consequences include:

Component	Effect
PHY Chip	Increased thermal output
Magnetics	Sustained current through transformers
Port ASICs	Frame buffer exhaustion

Surprisingly, most enterprise-grade equipment can sustain this condition indefinitely without hardware failure due to robust power regulation.

When facing unexplained network issues:

1. Topology verification (CDP/LLDP neighbors)
2. Switch port utilization monitoring
3. Broadcast domain segmentation with VLANs

Remember that unmanaged hubs (like in our case) don't participate in loop prevention protocols, making them particularly dangerous in modern networks.