Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR

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Chapter 8 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling

Configuring Layer 2 Protocol Tunneling

You can enable Layer 2 protocol tunneling (by protocol) on the ports that are connected to the customer

in the edge switches of the service-provider network. The service-provider edge switches connected to

the customer switch perform the tunneling process. Edge-switch tunnel ports are connected to customer

802.1Q trunk ports. Edge-switch access ports are connected to customer access ports. The edge switches

connected to the customer switch perform the tunneling process.

You can enable Layer 2 protocol tunneling on ports that are configured as access ports, tunnel ports, or

trunk ports. The switch supports Layer 2 protocol tunneling for CDP, STP, and VTP. The switch does not

support PAgP, LACP, and UDLD protocols for emulated point-to-point network topologies or Layer 2

protocol tunneling for LLDP.

When the Layer 2 PDUs that entered the service-provider inbound edge switch through a Layer 2

protocol-enabled port exit through the trunk port into the service-provider network, the switch

overwrites the customer PDU-destination MAC address with a well-known Cisco proprietary multicast

address (01-00-0c-cd-cd-d0). If 802.1Q tunneling is enabled, packets are also double-tagged; the outer

tag is the customer metro tag, and the inner tag is the customer’s VLAN tag. The core switches ignore

the inner tags and forward the packet to all trunk ports in the same metro VLAN. The edge switches on

the outbound side restore the proper Layer 2 protocol and MAC address information and forward the

packets to all Layer 2 protocol-enabled access ports, tunnel ports, and trunk ports in the same metro

VLAN. Therefore, the Layer 2 PDUs remain intact and are delivered across the service-provider

infrastructure to the other side of the customer network.

See Figure 8-5, 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.

These sections contain this configuration information:

• Default Layer 2 Protocol Tunneling Configuration, page 8-13

• Layer 2 Protocol Tunneling Configuration Guidelines, page 8-14

• Configuring Layer 2 Protocol Tunneling, page 8-15

Default Layer 2 Protocol Tunneling Configuration

Table 8-1 shows the default Layer 2 protocol tunneling configuration.

Table 8-1 Default Layer 2 Ethernet Interface VLAN Configuration

Feature Default Setting

Layer 2 protocol tunneling Disabled.

Shutdown threshold None set.