===== VLANs =====

  * Commands
    * show vlan internal usage
    * show vlan
  * Overview of VLANs
    * Breaks up collision domains into multiple broadcast domains
    * Layer 3 switches allow VLANs to communicate with each other
    * VTP version 3 updates do not pass through promiscuous trunk ports.
  * VLAN Configuration Guidelines and Restrictions
    * Prior to creating a VLAN, the switch must be in either VTP server or VTP transparent mode
      * In order to use VTP server mode, the VTP domain name must be prior defined
    * VLANs are organized into three ranges:
      * Reserved
      * Normal
      * Extended

^ VLANs ^ Range	^ Usage ^ Propagated by VTP ^
| 0, 4095   | Reserved  | For system use only. You cannot see or use these VLANs. | N/A |
| 1         | Normal    | Cisco default. You can use this VLAN but you cannot delete it. | Yes |
| 2-1001    | Normal    | Used for Ethernet VLANs; you can create, use, and delete these VLANs. | Yes |
| 1002-1005 | Normal    | Cisco defaults for FDDI and Token Ring. You cannot delete VLANs 1002-1005 | Yes |
| 1006-4094 | Extended  | For Ethernet VLANs only. When configuring extended-range VLANs, note the following: **1.** Layer 3 ports and some software features require internal VLANs. Internal VLANs are allocated from 1006 and up. You cannot use a VLAN that has been allocated for such use. To display the VLANs used internally, enter the show vlan internal usage command. **2.** Switches running Catalyst product family software do not support configuration of VLANs 1006-1024. If you configure VLANs 1006-1024, ensure that the VLANs do not extend to any switches running Catalyst product family software.You must enable the extended system ID to use extended range VLANs. | No |

  * Configurable Normal-Range VLAN Parameters
    * Note: VLANs 1 and 1006-4094 use only default values.
    * You can configure the following parameters for VLANs 2-1001:
      * VLAN name
      * VLAN type
      * VLAN state (active or suspended)
      * SAID
      * STP type for VLANs
  * VLAN Default Configuration
    * Ethernet VLAN Defaults and Ranges

^ Parameter ^ Default ^ Valid Values ^
| VLAN ID   | 1       | 1-4094       |
| VLAN name | VLANx, where x is a number assigned by the software. | No range |
| 802.10 SAID | 100,001 | 1-4,294,967,294 |
| MTU size | 1500 |1500-18,190 |
| Translational bridge 1 | 1002 | 0-1005 |
| Translational bridge 2 | 1003 | 0-1005 |
| VLAN state | active | active; suspend; shutdown |

  * Configuring VLANs
    * Stored in vlan.dat file
  * Configuring VLANs in Global Configuration Mode
    * When the switch boots, if the VTP domain name and VTP mode in the startup-config and vlan.dat files don't match, the switch uses the configuration in the vlan.dat file.