Trunking (also known as Tagging):

• Allow switches to pass vlan information between switches. And the port (interface) that allows vlan info to pass is called trunk link.
• Vlan no. is added to packet to recognize which vlan that packet belongs to. (total vlan numbers 0 to 4096)

Trunking Protocol:              

• 802.1Q {industry standard (can also be used for switches other than CISCO)
• ISL (Inter Switch Link): only used in CISCO switch, not normally used now a days.

 

S1(config)#int fa 0/24
S1(config-if)#switchport mode trunk

VTP (VlanTrunking Protocol):

• layer 2 protocol
• developed by cisco.
• is not a trunking protocol, it works over trunk links to replicate vlan database.
• send VTP advertisement every 5 minute or if there is a change in vlan database

 

Configuration:

• domain Name same
• version same (1,2)
• password same
• VTP mode (server/client/transparent)

 

VTP Modes:

Server (default):

• can add, modify, delete vlan info.
• send and receive vtp updates

Client:

• cannot add, modify, delete vlan info.
• receive updates from server and applies it to itself.
• send and receive vtp updates.

Transparent:

• cannot add, modify, delete vlan info.
• nor they send their updates to other switch, neither applies updates from other switch
  (but forward VTP updates received from other switch)

 

S# show  vtp  status

S1(config)#int fa 0/24
S1(config-if)#switchport mode trunk

S2(config)#int fastEthernet 0/24
S2(config-if)#switchport mode trunk

S1(config)#vtp domain alam
S1(config)#vtp password cisco

S2(config)#vtp domain alam
S2(config)#vtp mode client
S2(config)#vtp password cisco

[Now create a vlan 10 on S1, it will automatically be updated in S2. and if you try to create vlan on S2, it will be not allowed.]