9-9
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 9 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling
Understanding Layer 2 Protocol Tunneling
interface POS1
no ip address
crc 32
!
interface POS1.1
encapsulation dot1Q 10
bridge-group 10
!
interface POS1.3
encapsulation dot1Q 30
bridge-group 30
Example 9-5 applies to ML-Series card C.
Example 9-5 ML-Series Card C Configuration
hostname ML-C
bridge 10 protocol rstp
!
!
interface GigabitEthernet0
no ip address
no ip route-cache
mode dot1q-tunnel
bridge-group 10
bridge-group 10 spanning-disabled
!
interface POS0
no ip address
no ip route-cache
crc 32
!
interface POS0.1
encapsulation dot1Q 10
no ip route-cache
bridge-group 10
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 w ell as the local sites. Spanning Tree
Protocol (STP) must run properly, and every VLAN should build a proper spanning tree that in cludes 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. CDP, STP, or VTP Layer 2 protocol data units (PDUs) 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
the following results:
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.