Dot1Q has less overhead and support more vlan(s). Currently everyone is using dot1q (IEEE 802.1Q). Here note that, isl (Inter Switch Link) is a Cisco proprietary protocol but it’s old. Therefore, you need to put below command to allow trunk. Command rejected: An interface whose trunk encapsulation is "Auto" can not be configured to "trunk" mode. You can verify it “show interfaces switchport” command. When we put switchport mode as trunk, we will get a rejection message if we have trunk encapsulation mode as auto. Letsconfig-SW-01(config-if)#switchport mode trunk So, let’s configure trunk – letsconfig-SW-01#conf t It’s because we need to exchange VLAN database between switches to allow VLAN users to communicate each other. But in this example, we need to configure multiple VLANs (VLAN-10 and VLAN-20) in gig-0/3 interface on both switches. Still now, we have assigned a single VLAN on an interface and seems like everything is OK. Letsconfig-SW-01# letsconfig-SW-02#show vlan Letsconfig-SW-02(config-if)#switchport access vlan 20 Letsconfig-SW-02(config-if)#switchport access vlan 10 Letsconfig-SW-02(config-if)#switchport mode access Letsconfig-SW-02(config-vlan)#name vlan-20 letsconfig-SW-02(config)#int gig0/0 Letsconfig-SW-02(config-vlan)#name vlan-10 Similarly, we will configure our 2nd switch (letsconfig-SW-02) and verify the output. So, according VLAN fundamental, PC-1 and PC-2 will not be able to communicate with PC-3 and PC-4 because they are on different VLAN, however, they will be communicating with each other (PC-1 to PC-2 and PC-3 to PC-4). Interface Gi0/0, Gi0/1 is now under vlan 10 and Gi0/2, Gi0/3 is now under 20. Here is our new output – letsconfig-SW#show vlanġ default active Gi1/0, Gi1/1, Gi1/2, Gi1/3 Letsconfig-SW(config)#int gigabitEthernet 0/3 Letsconfig-SW(config-if)#switchport access vlan 20 Letsconfig-SW(config)#int gigabitEthernet 0/2 Letsconfig-SW(config)#int gigabitEthernet 0/1 We have assigned VLAN 10 on interface GigabitEthernet0/0.Ĭonfiguration for other interfaces are below – Letsconfig-SW(config-if)#switchport access vlan 10 Letsconfig-SW(config-if)#switchport mode access Letsconfig-SW(config)#interface GigabitEthernet0/0 Let’s configure vlan interfaces for our workstations. However, no interfaces are assigned to them. Let’s verify the output using “show vlan” command letsconfig-SW#show vlan However, now We will configure VLAN 10, 20 according our LAN topology diagram. Important to point out here, you cannot delete vlan 1 using “no vlan 1” command, to remove vlan 1 you need to delete vlan database using “delete flash:vlan.dat” command. Because of the same VLAN, we can communicate when a switch newly installed in a network. Here we can see, VLAN 1 is assigned for all interfaces.