1. VLAN Trunking Protocol
VTP
Inter-VLAN Routing

2. 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)

3. 802.1q Frame Tagging
VLAN identifier inserted into layer 2 frame

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

5. 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

6. 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

7. 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

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

9. 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