VLAN Trunking Protocol VTP Inter-VLAN Routing

What is VLAN Trunking? A physical and logical connection between two switches The trunk can carry the traffic of multiple VLANs Mechanism must be provided to identify VLAN membership on the trunk link Tagging (802.1q) Encapsulation (ISL)

802.1q Frame Tagging VLAN identifier inserted into layer 2 frame

ISL Encapsulation Ethernet frame is encapsulated with ISL header and modified FCS Results in non-standard frame size Not-interoperable with non-Cisco equipment

IOS Trunk Commands 1 Configuring trunk Links Switch(config-if)#switchport mode trunk Switch(config-if)#switchport trunk encapsulation dot1q OR Switch(config-if)#switchport trunk encapsulation isl 2 Verifying trunk links Switch#show trunk

VTP Overview Protocol to ensure that switches under common administrative control have consistent VLAN configuration & reduces complexity VTP messages encapsulated in ISL or dot1q frames Switches have 3 VTP modes Server – add, modify, delete VLANs Client – process VLAN changes and forward VTP messages Transparent – forward VTP messages only

Types of VTP messages Advertisement requests Summary Advertisements Request from client switches for VLAN information Summary Advertisements VTP servers issue summary advertisements every 5 minutes with revision number Clients which receive a summary advertisement with higher revision number than current create advertisement request Subset advertisements Information from server about VLAN configuration

Inter-VLAN routing Each VLAN in separate layer 3 broadcast domain Router needed to switch packets between VLANs

Using sub-interfaces If you have 3 VLANs but only 1 router port Create a trunk port on the switch Connect to router port Configure sub-interfaces on the router Does not work on 10Mbps interfaces