vlan-hopping-attack

name	vlan-hopping-attack
description	Simulates VLAN hopping attacks using switch spoofing and double tagging techniques in authorized environments to test VLAN segmentation effectiveness and validate switch port security configurations against Layer 2 bypass attacks.
domain	cybersecurity
subdomain	network-security
tags	["network-security","vlan-hopping","layer2-attack","switch-security","802.1q"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.IR-01","DE.CM-01","ID.AM-03","PR.DS-02"]

Performing VLAN Hopping Attack

When to Use

• Testing the effectiveness of VLAN-based network segmentation during authorized penetration tests
• Validating that switch trunk port configurations prevent unauthorized VLAN access
• Assessing whether 802.1Q tagging and native VLAN configurations resist double-tagging attacks
• Demonstrating to network teams why proper switch hardening is critical for isolation between zones
• Verifying that DTP (Dynamic Trunking Protocol) is disabled on all access ports

Do not use on production switches without explicit authorization and change management approval, against critical infrastructure VLANs (SCADA, medical devices) without safety controls, or as a denial-of-service vector.

Prerequisites

• Written authorization specifying in-scope VLANs and switches for testing
• Physical or virtual access to a switch access port on the target network
• Yersinia, Scapy, and frogger VLAN hopping tools installed on Kali Linux
• Understanding of 802.1Q trunking, DTP, and VLAN tagging at the frame level
• Access to switch CLI for verification of configurations (read-only is sufficient)
• Wireshark for capturing and verifying tagged frames

Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

Workflow

Step 1: Enumerate VLAN Configuration

# Identify the current VLAN assignment of the attacker port
ip link show eth0
cat /proc/net/vlan/config 2>/dev/null

# Use CDP/LLDP to discover switch information
sudo tcpdump -nn -v -i eth0 -s 1500 -c 1 'ether proto 0x88cc' 2>/dev/null
# Or use lldpd
lldpcli show neighbors

# If CDP is enabled, capture CDP frames
sudo tcpdump -nn -v -i eth0 -s 1500 -c 1 'ether[20:2] == 0x2000'

# Use Yersinia to discover DTP and VTP information
sudo yersinia -G &
# Or command line:
sudo yersinia dtp -attack 0 -interface eth0
# This listens for DTP frames to learn trunk negotiation status


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