Understanding Layer 2 Protocol Tunneling - Cisco Catalyst 3750 Software Configuration Manual

Understanding Layer 2 Protocol Tunneling

Command
Step 3 switchport vlan mapping dot1qtunnel
outer-vlan-id {inner-vlan-id
translated-vlan-id | drop}
Step 4 end
Step 5
show vlan mapping
Step 6
copy running-config startup-config
Use the no switchport vlan mapping dot1qtunnel outer-vlan-id {inner-vlan-id translated-vlan-id |
drop} interface configuration command to remove the mapping information.
This example shows how to configure the ES port so that 802.1Q traffic with the outer VLAN ID 5 and
the inner VLAN ID 6 would leave the switch with the single VLAN ID of 10. The 802.1Q traffic with
the outer VLAN 5 and any inner VLAN ID other than 6 would be dropped. Other traffic on VLAN 5
would also be dropped:
Switch(config)# interface gigabiethernet1/1/1
Switch(config-if)# switchport vlan mapping dot1q-tunnel 5 6 10
Switch(config-if)# switchport vlan mapping dot1q-tunnel 5 drop
Switch(config-if)# exit

Understanding Layer 2 Protocol Tunneling

Customers at different sites connected across a service-provider network need to run various Layer 2
protocols to scale their topology to include all remote sites, as well as the local sites. STP must run
properly, and every VLAN should build a proper spanning tree that includes the local site and all remote
sites across the service-provider infrastructure. Cisco Discovery Protocol (CDP) must discover
neighboring Cisco devices from local and remote sites. VLAN Trunking Protocol (VTP) must provide
consistent VLAN configuration throughout all sites in the customer network.
When protocol tunneling is enabled, edge switches on the inbound side of the service-provider
infrastructure encapsulate Layer 2 protocol packets with a special MAC address and send them across
the service-provider network. Core switches in the network do not process these packets but forward
them as normal packets. Layer 2 protocol data units (PDUs) for CDP, STP, or VTP cross the
service-provider infrastructure and are delivered to customer switches on the outbound side of the
service-provider network. Identical packets are received by all customer ports on the same VLANs with
these results:
•
•
Catalyst 3750 Metro Switch Software Configuration Guide
13-10
Purpose
Specify the action to be taken if the outer VLAN ID of the original 802.1Q
packet matches the specified value:
Return to privileged EXEC mode.
Verify the configuration.
(Optional) Save your entries in the configuration file.
Users on each of a customer's sites are able to properly run STP, and every VLAN can build a correct
spanning tree based on parameters from all sites and not just from the local site.
CDP discovers and shows information about the other Cisco devices connected through the
service-provider network.
Chapter 13
• outer-vlan-id —Enter the outer VLAN ID of the original 802.1Q
packet.
• inner-vlan-id translated-vlan-id —Enter the inner VLAN ID of the
original 802.1Q packet and the translated VLAN ID for the
service-provider network. The VLAN ID range is from 1 to 4094.
drop—Specify that traffic with the specified outer VLAN ID is
•
dropped unless the inner VLAN ID is matched in the existing VLAN
mappings.
Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
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