The l2protocol-tunnel group-mac command configures a device to replace the multicast destination MAC addresses in Layer 2 protocol data units (PDUs) with a specified multicast MAC address (group MAC address).
The undo l2protocol-tunnel group-mac command deletes the specified multicast MAC address (group MAC address) from Layer 2 PDUs of all Layer 2 protocols except STP or restores the default multicast MAC address in STP BPDUs.
By default, Layer 2 PDUs of all Layer 2 protocols do not have a default group MAC address.
| Parameter | Description | Value |
|---|---|---|
| protocol |
Replaces the destination MAC address in Layer 2 PDUs of a specified protocol with a specified multicast MAC address. |
The protocol as follows:
One or up to all of the preceding Layer 2 protocols can be specified. |
| group-mac group-mac |
Specifies the multicast MAC address which is used to replace the destination MAC address in Layer 2 PDUs. |
The value is a 12-digit hexadecimal number, in the format of H-H-H. Each H is 4 digits. If an H contains fewer than 4 digits, the left-most digits are padded with zeros. For example, e0 is displayed as 00e0. group-mac must start with 0x01 and cannot be any of the following multicast MAC addresses:
|
Usage Scenario
Some Layer 2 protocols running between user networks, such as Multiple Spanning Tree Protocol (MSTP) and Link Aggregation Control Protocol (LACP), must traverse a backbone network to perform Layer 2 protocol calculation.
Generally, the destination MAC addresses in Layer 2 PDUs of the same Layer 2 protocol are the same. For example, the MSTP PDUs have a destination MAC address 0180-C200-0000. When a Layer 2 PDU reaches an edge device on a backbone network, the edge device cannot identify whether the PDU comes from a user network or the backbone network and sends the PDU to the CPU to calculate a spanning tree. As a result, the user network devices calculate a spanning tree with backbone network edge devices but not with user network devices. To resolve this problem, run the l2protocol-tunnel group-mac command on backbone network edge devices to replace the multicast destination MAC addresses in Layer 2 PDUs with a specified multicast MAC address (group MAC address). This configuration allows Layer 2 PDUs to be tunneled so that user network devices can calculate a spanning tree.Follow-up Procedure
The backbone network edge devices determine whether to add an outer VLAN tag to the Layer 2 PDUs with a specified multicast MAC address (group MAC address) based on the configured Layer 2 protocol tunneling type.
Precautions
The specified multicast MAC address cannot be a multicast MAC address used by well-known protocols.
In VS mode, this command is supported only by the admin VS.