16-11
Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide
OL-12247-01
Chapter 16 Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling
Configuring Layer 2 Protocol Tunneling
See
Figure 16-4
, with Customer X and Customer Y in access VLANs 30 and 40, respectively.
Asymmetric links connect the customers in Site 1 to edge switches in the service-provider network. The
Layer 2 PDUs (for example, BPDUs) coming into Switch B from Customer Y in Site 1 are forwarded to
the infrastructure as double-tagged packets with the well-known MAC address as the destination MAC
address. These double-tagged packets have the metro VLAN tag of 40, as well as an inner VLAN tag
(for example, VLAN 100). When the double-tagged packets enter Switch D, the outer VLAN tag 40 is
removed, the well-known MAC address is replaced with the respective Layer 2 protocol MAC address,
and the packet is sent to Customer Y on Site 2 as a single-tagged frame in VLAN 100.
You can also enable Layer 2 protocol tunneling on access ports on the edge switch connected to access
or trunk ports on the customer switch. In this case, the encapsulation and decapsulation process is the
same as described in the previous paragraph, except that the packets are not double-tagged in the
service-provider network. The single tag is the customer-specific access VLAN tag.
In switch stacks, Layer 2 protocol tunneling configuration is distributed among all stack members. Each
stack member that receives an ingress packet on a local port encapsulates or decapsulates the packet and
forwards it to the appropriate destination port. On a single switch, ingress Layer 2 protocol-tunneled
traffic is sent across all local ports in the same VLAN on which Layer 2 protocol tunneling is enabled.
In a stack, packets received by a Layer 2 protocol-tunneled port are distributed to all ports in the stack
that are configured for Layer 2 protocol tunneling and are in the same VLAN. All Layer 2 protocol
tunneling configuration is handled by the stack master and distributed to all stack members.
These sections contain this configuration information:
•
Default Layer 2 Protocol Tunneling Configuration, page 16-11
•
Layer 2 Protocol Tunneling Configuration Guidelines, page 16-12
•
Configuring Layer 2 Protocol Tunneling, page 16-13
•
Configuring Layer 2 Tunneling for EtherChannels, page 16-14
Default Layer 2 Protocol Tunneling Configuration
Table 16-1
shows the default Layer 2 protocol tunneling configuration.
Table 16-1
Default Layer 2 Ethernet Interface VLAN Configuration
Feature
Default Setting
Layer 2 protocol tunneling
Disabled.
Shutdown threshold
None set.
Drop threshold
None set.
CoS value
If a CoS value is configured on the interface for data packets, that
value is the default used for Layer 2 PDUs. If none is configured,
the default is 5.
