Configuring VTP and VLANs on Cisco switches 
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Public domain
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### Concepts

**VLAN:** A virtual local area network, virtual LAN or VLAN, is a group of hosts with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical local area network (LAN), but it allows for end stations to be grouped together even if they are not located on the same network switch. VLAN membership can be configured through software instead of physically relocating devices or connections. (Wikipedia)

**Trunk:** A trunk link carries multiple VLANs through a single network link through the use of a "trunking protocol". (Wikipedia)

**802.1Q:** To allow for multiple VLANs on one link, frames from individual VLANs must be identified by a "trunking protocol". The most common and preferred method, IEEE 802.1Q adds a tag (4 bytes) to the Ethernet frame header, labeling it as belonging to a certain VLAN. (Wikipedia)

**Native VLAN:** If a switch receives untagged frames on a trunkport, they are assumed to be part of the vlan that are designated on the switchport as the native vlan.

**VTP:** VLAN Trunking Protocol (VTP) is a Layer 2 messaging protocol that propagates the definition of VLANs on the whole local area network. To do this, VTP carries VLAN information to all the switches in a VTP domain. VTP only works over trunk links. This includes Inter-Switch Link(ISL), IEEE 802.1q, and LAN emulation (LANE) trunks.  (Wikipedia)

**VTP Server:** The VTP Server can add, delete or rename VLANS. It also advertises the domain name, The VLAN configuration and configuration revision number to all other switches in the VTP domain. It maintains a list of all VLANS in the domain in NVRAM and can retrieve this information even if switch reset occurs. The advertisements is sent to a special destination multicast MAC address 01-00-0C-CC-CC-CC.

**VTP CLient:** A VTP Client can not add, delete or rename VLANS. It maintains a list ot all VLANS in the domain, but does not store them.

**VTP Transparent:** A VTP Transparent switch must have its VLANS configured manually. Changes to VLAN configuration are not propagated to other switches. It will still relay VTP messages over its trunk links to other switches if it is in the same VTP domain or in a null VTP domain.

**VTP Pruning:** VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even though receiving switches might discard them. (Cisco)

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### Monitoring VTP

    show vtp status
    show vtp counters

### Configuring VTP Server

    configure terminal
    vtp domain SW_DOMAIN1
    vtp password 123456
    vtp mode server
    vtp pruning
    end

### Resetting the VTP configuration revision number on clients

    show vtp status
    ! Write down the domain name. 
    ! Write down the configuration revision number. 
    configure terminal
    vtp domain TEMPNAME 
    end
    show vtp status
    configure terminal 
    ! Restore original domain name.
    vtp domain domain-name
    end

### Configuring VTP Client 

    configure terminal
    vtp domain SW_DOMAIN1 
    vtp password 123456
    vtp mode client
    end

### Checking defined VLANs

    show vlan
    show vlan brief

### Checking vlan database (vlan.dat)

    show flash

### Checking trunks

    show running-config interface gigabitEthernet 1/0/1
    show interfaces gigabitEthernet 1/0/1 switchport
    show interfaces gigabitEthernet 1/0/1 trunk
    show interfaces trunk

### Configuring trunk ports

    configure terminal
    interface range gigabitEthernet 1/0/1 - 4
    switchport trunk encapsulation dot1q
    switchport mode trunk
    switchport nonegotiate
    no shutdown
    end

### Configuring access ports

    configure terminal
    interface range fastEthernet 1/0/1 - 48
    switchport mode access
    no cdp enable
    end

### Creating VLANs - old way

    enable
    vlan database
    vlan 100 name USERS 
    apply
    end

### Creating VLANs - new way

    configure terminal
    vlan 100
    name USERS
    end

### Assigning ports to VLANs

    configure terminal
    interface fastEthernet 1/0/1
    switchport mode access
    no cdp enable
    switchport access vlan 100
    end

### Configuring management VLAN

    configure terminal
    ! Disable default VLAN 1
    interface vlan 1
    no ip address
    shutdown
    exit
    ! Create new VLAN 2 for management
    vlan 2
    name MANAGEMENT
    exit
    ! Assigin IP address to management VLAN 2
    interface vlan 2
    ip address 172.31.0.1 255.255.255.0
    no shutdown
    end

### Configuring native VLAN

    configure terminal
    ! Create new VLAN 3 for native VLAN use
    vlan 3
    name NATIVE
    exit
    ! Configuring VLAN 3 as native on trunk ports
    interface range gigabitEthernet 1/0/1 - 4
    switchport trunk encapsulation dot1q
    switchport mode trunk
    switchport nonegotiate
    switchport trunk native vlan 3
    no shutdown
    end
 
### Control what VLANs can pass through trunk ports


    configure terminal
    interface range gigabitEthernet 1/0/1 - 4
    switchport trunk encapsulation dot1q
    switchport mode trunk
    switchport nonegotiate
    switchport trunk native vlan 3
    switchport trunk allowed 10,20,30
    no shutdown
    end

### Clearing switch config

    write erase
    delete flash:vlan.dat

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_BY: Pejman Moghadam_  
_TAG: vlan, trunk, vtp_  
_DATE: 2012-02-01 23:03:08_