l2protocol-tunnel group-mac
Function
The l2protocol-tunnel group-mac command enables the switch to replace the multicast destination MAC address of Layer 2 protocol packets with a specified multicast MAC address.
The undo l2protocol-tunnel command disables the group MAC function for Layer 2 protocol tunneling. After you run this command, the switch deletes a configured multicast destination MAC address of Layer 2 protocol packets except STP packets that uses the default multicast destination address or restores the default multicast destination MAC address of STP packets.
By default, the multicast destination MAC address of STP packets is replaced by 0100-0ccd-cdd0. For other Layer 2 protocol packets, there is not a default multicast MAC address for replacing their multicast destination MAC addresses.
Format
l2protocol-tunnel protocol-type group-mac { group-mac | default-group-mac }
undo l2protocol-tunnel protocol-type
Parameters
Parameter |
Description |
Value |
|---|---|---|
protocol-type |
Specifies the type of a Layer 2 protocol. |
The protocol type can be:
|
group-mac |
Specifies the multicast MAC address that replaces the destination MAC address of Layer 2 protocol packets. |
The value is in H-H-H format. An H is a hexadecimal number of 1 to 4 digits. The value ranges from 0100-0000-0000 to 01ff-ffff-ffff. |
default-group-mac |
Specifies the default MAC address of a multicast group, which is 0100-0ccd-cdd0. |
- |
Usage Guidelines
Usage Scenario
Layer 2 protocols running between user networks, such as MSTP, HGMP, and LACP, must traverse a backbone network to perform Layer 2 protocol calculation.
Generally, the destination MAC addresses in Layer 2 protocol packets of the same Layer 2 protocol are the same. For example, the MSTP PDUs are BPDUs with the destination MAC address 0180-C200-0000. Therefore, when a Layer 2 protocol packet reaches an edge device on a backbone network, the edge device cannot identify whether the Layer 2 protocol packet comes from a user network or the backbone network and sends the Layer 2 protocol packet 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 protocol packets with a specified multicast MAC address (group MAC address). This configuration allows Layer 2 protocol packets to be tunneled so that user network devices can calculate a spanning tree.
After this command is run, run the display l2protocol-tunnel statistics group-mac command to check statistics about the group-mac packets transparently transmitted by a specified interface.
Precautions
When configuring Layer 2 protocol tunneling, do not use the following multicast MAC addresses to replace the destination MAC address of Layer 2 protocol packets:
- Reserved multicast MAC addresses: 0180-C200-0000 to 0180-C200-002F
- Special multicast MAC addresses: 0100-0CCC-CCCC and 0100-0CCC-CCCD
- Destination MAC address of Smart Link packets: 010F-E200-0004
- Multicast MAC addresses that have been used on the network.
- Destination MAC address of VRRP packets: 0100-5E00-0012
Do not replace the destination MAC addresses of SSTP, STP, GVRP, and GMRP packets with the same multicast MAC address.