Cisco Catalyst 4500 Series Configuration Manual page 686

About Layer 2 Protocol Tunneling
VTP provides consistent VLAN configuration throughout the customer network, propagating to all
•
switches through the service provider.
Layer 2 protocol tunneling can enabled on trunk, access and tunnel ports. If protocol tunneling is not
enabled, remote switches at the receiving end of the service provider network do not receive the PDUs
and cannot properly run STP, CDP, and VTP. When protocol tunneling is enabled, Layer 2 protocols
within each customer's network are totally separate from those running within the service provider
network.
As an example, Customer A in
through the service provider network. If the network does not tunnel PDUs, switches on the far ends of
the network cannot properly run STP, CDP, and VTP. For example, STP for a VLAN on a switch in
Customer A's Site 1 builds a spanning tree on the switches at that site without considering convergence
parameters based on Customer A's switch in Site 2.
topology.
Figure 27-6
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
27-14
Chapter 27
Figure 27-6
Layer 2 Protocol Tunneling
Customer A Site 1
VLANs 1 to 100
VLAN 30
VLAN 30
Switch 1
Switch 1
Switch 2
VLAN 40
Customer B Site 1
VLANs 1 to 200
Configuring 802.1Q Tunneling, VLAN Mapping, and Layer 2 Protocol Tunneling
has four switches in the same VLAN that are connected
Figure 27-6 shows one possible spanning tree
Service
provider
Trunk
Trunk
ports
ports
Trunk
Trunk
ports ports
VLAN 40
Trunk
Asymmetric link
Customer A Site 2
VLANs 1 to 100
VLAN 30
Switch 3
Switch 4
Customer B Site 2
VLANs 1 to 200
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