Understanding VLAN Hopping and Network Security

VLAN hopping is a network attack where an attacker gains unauthorized access to traffic on a VLAN that is not their own. This can be achieved through switch spoofing or double tagging.

How VLAN Hopping Works

1. Switch Spoofing: The attacker configures their device to act as a switch, tricking the network into allowing VLAN traffic.
2. Double Tagging: The attacker adds two VLAN tags to a packet, bypassing the first switch’s VLAN restrictions.

You Should Know: Preventing VLAN Hopping

Here are key commands and configurations to secure your network against VLAN hopping:

1. Disable Dynamic Trunking Protocol (DTP)

DTP can be exploited to negotiate trunk links. Disable it on all non-trunk ports:

switch(config) interface gigabitethernet 0/1 
switch(config-if) switchport mode access 
switch(config-if) switchport nonegotiate 

2. Use VLAN Access Control Lists (VACLs)

Restrict inter-VLAN communication:

switch(config) vlan access-map BLOCK-HOPPING 10 
switch(config-access-map) match ip address 101 
switch(config-access-map) action drop 
switch(config) vlan filter BLOCK-HOPPING vlan-list 10,20 

3. Enable Port Security

Limit MAC addresses per port:

switch(config-if) switchport port-security 
switch(config-if) switchport port-security maximum 2 
switch(config-if) switchport port-security violation restrict 

4. Implement Private VLANs (PVLANs)

Isolate devices within the same VLAN:

switch(config) vlan 100 
switch(config-vlan) private-vlan primary 
switch(config-vlan) private-vlan association 101,102 

5. Monitor for Unauthorized VLAN Changes

Use logging to detect VLAN modifications:

switch(config) logging host 192.168.1.10 
switch(config) logging trap notifications 

Expected Output: Secure VLAN Configuration

After applying these measures, verify your settings:

switch show vlan brief 
switch show interfaces trunk 
switch show port-security 

What Undercode Say

VLAN hopping remains a critical threat in poorly configured networks. Always:
– Disable unused ports (shutdown).
– Use strong authentication (802.1X).
– Regularly audit VLAN assignments (show vlan).
– Segment sensitive traffic (PCI, HIPAA).

Expected Output: A hardened network resistant to VLAN hopping attacks.

(No relevant URLs extracted from the original post.)

References:

Reported By: Slijderink Free – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

Join Our Cyber World:

💬 Whatsapp | 💬 Telegram