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VLAN Trunking Protocol. Trunking 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)
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VLAN Trunking Protocol Trunking 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 mode trunk 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 • 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