Users Guide

consumed and later dropped because the intermediate network itself might be using spanning tree (shown in the following
illustration).
Figure 126. 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).
Service Provider Bridging 865