Dell S6100 Configuration Manual page 808

Figure 119. VLAN Stacking without L2PT
You might need to transport control traffic transparently through the intermediate network to the other region. Layer 2 protocol tunneling
enables BPDUs to traverse the intermediate network by identifying frames with the Bridge Group Address, rewriting the destination MAC
to a user-configured non-reserved address, and forwarding the frames. Because the frames now use a unique MAC address, BPDUs are
treated as normal data frames by the switches in the intermediate network core. On egress edge of the intermediate network, the MAC
address rewritten to the original MAC address and forwarded to the opposing network region (shown in the following illustration).
Dell Networking OS Behavior: In Dell Networking OS versions prior to 8.2.1.0, the MAC address that Dell Networking systems use to
overwrite the Bridge Group Address on ingress was non-configurable. The value of the L2PT MAC address was the Dell Networking-unique
MAC address, 01-01-e8-00-00-00. As such, with these Dell Networking OS versions, Dell Networking systems are required at the egress
edge of the intermediate network because only Dell Networking OS could recognize the significance of the destination MAC address and
rewrite it to the original Bridge Group Address. In Dell Networking OS version 8.2.1.0 and later, the L2PT MAC address is user-configurable,
so you can specify an address that non-Dell Networking systems can recognize and rewrite the address at egress edge.
808 Service Provider Bridging