14.9.11 Packet Tracer - Layer 2 Vlan Security Apr 2026

In the world of networking, we often talk about firewalls, ACLs, and encryption. But what happens if an attacker simply unplugs a legitimate user’s laptop and plugs in a rogue device? What if they spoof a VLAN or launch a MAC flood?

interface g0/1 switchport trunk native vlan 999 Then, ensure VLAN 999 exists but is used nowhere else. No user devices, no DHCP, no routing.

Cisco’s Packet Tracer activity is an excellent, hands-on lab that forces you to think like both a network admin and a hacker. It focuses on three critical Layer 2 vulnerabilities and their mitigations: MAC Flooding , VLAN Hopping (Switch Spoofing) , and DHCP Starvation .

Take the time to run this lab. Break it on purpose. Watch the show port-security , show dhcp snooping binding , and show interfaces status err-disabled outputs. 14.9.11 packet tracer - layer 2 vlan security

The four techniques in form the backbone of the Cisco Cyber Threat Defense model:

ip dhcp snooping ip dhcp snooping vlan 10,20 interface g0/1 ip dhcp snooping trust interface range fa0/1-24 ip dhcp snooping limit rate 10 no ip dhcp snooping trust Now, only the uplink port can send DHCP Offer/ACK messages. Any rogue server on an access port will be ignored.

That’s where comes in. It’s the often-overlooked foundation of network defense. In the world of networking, we often talk

interface g0/1 switchport mode trunk switchport nonegotiate If a port is for a user, it should be an access port, period. Don't let devices negotiate their way into privilege. Step 3: Changing the Native VLAN (Double Tagging Defense) The Threat: In a double-tagging attack, the attacker sends a frame with two 802.1Q tags. The first tag (native VLAN) is stripped off by the first switch. The second tag (say, VLAN 10) is then visible to the next switch, potentially letting the attacker hop into a restricted VLAN.

Never use VLAN 1 for anything. Not for native VLAN, not for management, not for users. VLAN 1 is the universal key to many Layer 2 attacks. Step 4: DHCP Snooping – Stopping the Rogue Server The Threat: An attacker plugs in a laptop running a rogue DHCP server. When legitimate clients broadcast for an IP, the rogue server replies first, giving them a malicious gateway (the attacker) or a bogus DNS server (phishing).

| Threat | Mitigation | | :--- | :--- | | MAC Flooding | Port Security | | VLAN Hopping (DTP) | switchport mode access / nonegotiate | | Double Tagging | Non-default native VLAN | | Rogue DHCP | DHCP Snooping | Packet Tracer 14.9.11 is not just about passing a skills exam—it's about building an operator mindset . The best router ACL in the world is useless if an attacker can sit on your switch and sniff everything. interface g0/1 switchport trunk native vlan 999 Then,

Disable DTP and set trunking manually.

Port Security.

On any port that should not be a trunk (i.e., all end-user ports), explicitly turn off trunking:

Happy (secure) switching.