1. Trunk Encapsulation
   1. IEEE 802.1Q
      1. Inserts VLAN tag between Source MAC and Type field
      2. Header Size: 4 bytes
      3. Max VLANs: 4094
   2. Cisco ISL
      1. Adds ISL header before Dest MAC and ISL FCS after Type field
      2. Header Size: 26 bytes
      3. Trailer Size: 4 bytes
      4. Max VLANs: 1000
   3. Untagged
      1. Normal Ethernet Frame:
         1. Dest MAC (6 bytes)
         2. Source MAC (6 ytes)
         3. Type (2 bytes)
2. Terminology
   1. Trunking
      1. Carrying multiple VLANs over the same physical connection
   2. Native VLAN
      1. IEEE 802.1Q) By default, frames in this VLAN are untagged when sent across a trunk
   3. Access VLAN
      1. The VLAN to which an access port is assigned
   4. Voice VLAN
      1. If configured, enables minimal trunking to support voice traffic in addition to data traffic on an access port
   5. Dynamic Trunking Protocol (DTP)
      1. Can be used to automatically establish trunks between capable ports (insecure)
   6. Switched Virtual Interface (SVI)
      1. A virtual interface which provides a routed gateway into and out of a VLAN
3. VLAN Configuration
   1. Create VLAN
      1. Switch(config)# vlan <vlan-num>
      2. Switch(config-vlan)# name <vlan-name>
   2. Assign port to VLAN
      1. Switch(config)# interface <interface>
      2. Switch(config-if)# switchport mode access
      3. Switch(config-if)# switchport access vlan <vlan-num>
   3. Configure trunk
      1. Switch(config)# interface type member/module/number
      2. Switch(config-if)# switchport trunk encapsulation {isl | dot1q | negotiate}
      3. Switch(config-if)# switchport trunk native vlan vlan-id
      4. Switch(config-if)# switchport trunk allowed vlan {vlan-list | all | {add | except | remove} vlan-list}
      5. Switch(config-if)# switchport mode {trunk | dynamic {desirable | auto}}
   4. Define the trunking on a port to a Cisco IP phone.
      1. Switch(config-if)# switchport voice vlan {vlan-id | dot1p | untagged | none}
4. VLAN Troubleshooting
   1. Displays the contents of the MAC address table
      1. show mac address-table [dynamic]
   2. Clears dynamically learned MAC addresses to determine whether a previously learned MAC address is relearned.
      1. clear mac address-table dynamic
   3. Shows to which VLANs the ports of a switch belong.
      1. show vlan brief
   4. Displays which VLANs are permitted on the trunk ports of a switch and which switchports are configured as trunks.
      1. show interfaces trunk
   5. Displays VLAN and trunk information related to a switchport.
      1. show interfaces interface_type interface_number switchport