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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)

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