VLAN hopping is a cyberattack technique that targets network resources on a Virtual Local Area Network (VLAN). This method allows an attacker to gain unauthorized access to traffic on other VLANs, which are typically isolated from each other for security purposes. By exploiting vulnerabilities in the network's VLAN configuration, the attacker can bypass these logical separations and access sensitive data or systems that would otherwise be out of reach.

How does VLAN Hopping Work?

VLAN hopping works primarily through two techniques: switch spoofing and double tagging. In switch spoofing, an attacker mimics a trunking switch by using protocols like Dynamic Trunking Protocol (DTP) to negotiate a trunk link with a legitimate switch. This allows the attacker to access multiple VLANs, as the trunk link carries traffic for all VLANs configured on the switch.

Double tagging involves the attacker sending Ethernet frames with two VLAN tags. The first switch removes the outer tag, which corresponds to the native VLAN, and forwards the frame. The second switch then processes the inner tag, directing the frame to the target VLAN. This method exploits the way switches handle VLAN tags, allowing the attacker to bypass VLAN isolation mechanisms.

What are Examples of VLAN Hopping?

Examples of VLAN hopping can be seen in scenarios where attackers exploit network configurations to gain unauthorized access. One common example involves switch spoofing, where an attacker configures their device to mimic a trunking switch. By doing so, they can negotiate a trunk link with a legitimate switch, allowing them to access multiple VLANs and intercept traffic that would otherwise be isolated.

Another example is double tagging, where an attacker sends Ethernet frames with two VLAN tags. The first switch removes the outer tag, which corresponds to the native VLAN, and forwards the frame. The second switch then processes the inner tag, directing the frame to the target VLAN. This method takes advantage of the way switches handle VLAN tags, enabling the attacker to bypass VLAN isolation mechanisms and access restricted network segments.

What are the Potential Risks of VLAN Hopping?

• Potential Data Breaches: VLAN hopping can lead to unauthorized access to network traffic on different VLANs, potentially exposing sensitive data.

• Unauthorized Access to Sensitive Information: Switch spoofing and double tagging attacks allow an attacker to access VLANs that should be isolated, leading to unauthorized access to sensitive information.

• Network Disruption: Such exploits can disrupt network operations by allowing malicious traffic to traverse VLAN boundaries, potentially leading to network instability or performance issues.

• Compromised Network Integrity: Attackers can gain unauthorized access to multiple VLANs, compromising the integrity of the network.

• Escalation of Privileges: VLAN hopping can lead to the escalation of privileges as attackers gain access to VLANs they should not have access to, effectively escalating their privileges within the network.

How can you Protect Against VLAN Hopping?

To protect against VLAN hopping, consider implementing the following measures:

• Disable Dynamic Trunking Protocol (DTP): Turn off DTP on all switch ports that do not require trunking to prevent unauthorized trunk link negotiations.

• Configure Access Ports: Set all non-trunk ports to access mode using the command switchport mode access to ensure they do not become trunk ports.

• Change Native VLAN: Assign an unused VLAN ID as the native VLAN on all trunk ports to prevent double tagging attacks.

• Explicitly Tag Native VLAN: Ensure the native VLAN is explicitly tagged on all trunk ports to maintain proper VLAN isolation.

• Implement Port Security: Use port security features to limit the number of MAC addresses on a port and disable unused ports to prevent unauthorized access.