TB - GNS3 Lab: VACL (VLAN Access Lists) with GNS3Vault

In this blog, I walk through the lab step-by-step and include screenshots to document my process and learning.

Using Rene Molenaar’s GNS3 Vault lab

🔒 Blocking Ping in the Same VLAN Using VACLs on a Cisco Switch

Have you ever needed to block ping (ICMP) traffic between two devices on the same VLAN, while still allowing other types of communication? Traditional router-based ACLs won’t help in this case, because Layer 2 switches forward traffic within the same VLAN without routing it.

That’s where VACLs (VLAN Access Control Lists) come in.

---

🧱 What Are VACLs?

VACLs apply access control policies within a VLAN, regardless of whether traffic is being bridged (switched) or routed. Unlike port-based ACLs (PACLs), which only apply to ingress traffic on a switchport, VACLs apply to all traffic within the specified VLAN(s).

This is especially useful for enforcing security policies between same-subnet hosts on a switch.

---

🧾 Lab Scenario

You have a topology like this:

• SW1 (Layer 2 switch)
• DNS1 connected to gi0/0, IP: 192.168.10.1
• DNS2 connected to gi0/1, IP: 192.168.10.2
• Both hosts are in VLAN 10

🎯 Goal: Prevent DNS1 and DNS2 from pinging each other (block ICMP), but allow all other traffic.

---

🔧 Step 1: Assign Ports to VLAN 10

Configure both switchports as access ports in VLAN 10.

conf t
interface gi0/0
 switchport mode access
 switchport access vlan 10
!
interface gi0/1
 switchport mode access
 switchport access vlan 10

---

🔧 Step 2: Create an Extended ACL

We’ll use an extended ACL to match ICMP traffic between the two hosts.

ip access-list extended BLOCK_ICMP
 deny icmp host 192.168.10.1 host 192.168.10.2
 deny icmp host 192.168.10.2 host 192.168.10.1
 permit ip any any

---

🔧 Step 3: Create a VLAN Access Map

Bind the ACL to an action using a VLAN access map.

vlan access-map FILTER_VLAN10 10
 match ip address BLOCK_ICMP
 action drop
!
vlan access-map FILTER_VLAN10 20
 action forward

---

🔧 Step 4: Apply the Access Map to VLAN 10

vlan filter FILTER_VLAN10 vlan-list 10

---

🔍 Verification Commands

Check your configuration using the following commands:

show vlan access-map
show vlan filter
show access-lists BLOCK_ICMP

---

🧪 Testing

1. From DNS1:

   ping 192.168.10.2
   

   ➡️ Should fail

2. Test other traffic (e.g., telnet, ssh) to confirm it still works. (I did not have the patience to configure telnet to make sure it worked so I stopped at making sure that the pings failed in this lab.)

---

✅ Result

• DNS1 and DNS2 cannot ping each other.
• All other communication is allowed.
• Filtering is enforced at Layer 2 using VLAN ACLs.

---

Happy switching! 🧠🔧