930 | Service Provider Bridgingw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Figure 44-13. VLAN Stacking without L2PTYou might need to transport control traffic transparently through the intermediate network to the otherregion. Layer 2 Protocol Tunneling enables BPDUs to traverse the intermediate network by identifyingframes with the Bridge Group Address, rewriting the destination MAC to a user-configured non-reservedaddress, and forwarding the frames. Since the frames now use a unique MAC address, BPDUs are treatedas normal data frames by the switches in the intermediate network core. On egress edge of the intermediatenetwork, the MAC address rewritten to the original MAC address and forwarded to the opposing networkregion (Figure 44-14).FTOS Behavior: In FTOS versions prior to 8.2.1.0, the MAC address that Dell Force10 systems use to overwritethe Bridge Group Address on ingress was non-configurable. The value of the L2PT MAC address was the DellForce10-unique MAC address, 01-01-e8-00-00-00. As such, with these FTOS versions, Dell Force10 systems arerequired at the egress edge of the intermediate network because only FTOS could recognize the significance ofthe destination MAC address and rewrite it to the original Bridge Group Address. In FTOS version 8.2.1.0 andlater, the L2PT MAC address is user-configurable, so you can specify an address that non-Dell Force10 systemscan recognize and rewrite the address at egress edge.INTERNETSERVRICEPROVIDERw/wwSPAPPNNINGTREESPAPPNNINGTREENETWORKSPAPPNNINGTREETREEBuilding ABuilding BXBPDU w/ destinationMAC address: 01-80-C2-00-00-00no spanning-tree no spanning-tree
