Principles

The Layer 2 DCN solution uses bridges to forward DCN data encapsulated into Ethernet frames.

1. After receiving DCN information encapsulated in standard Ethernet data frames, ports where the L2 DCN function is enabled check the frame length and discard frames with a length of more than 1518 bytes.
2. The bridge adds or updates the forwarding address items in its MAC address table, establishing mappings between source MAC addresses and destination MAC addresses.
3. The bridge checks the destination MAC addresses of the data frames in the MAC address table.
   • If the destination MAC address is the MAC address of the local NE, the bridge sends the data frames to the network layer for processing.
   • If the destination MAC address is not the MAC address of the local NE, the data frames are forwarded according to the following principles:
     • If the dynamic table items corresponding to the destination MAC address exist, the bridge forwards this data frames to the destination port in the table item.
     • If no table item corresponding to the destination MAC address exists, the bridge forwards the data frames to all ports (except the source port and the redundant port that is blocked by the RSTP protocol) where the L2 DCN function is enabled.

The following figure shows the procedure for L2 DCN: