Carrier Ethernet 83
Essentially, PBB employs an additional Service Provider 16 bit MAC address19 that
corresponds to the ingress Ethernet ports of the Service Provider edge device and basically
encapsulates the end user??™s MAC (this is also referred to as MAC-in-MAC). The
outer MAC address is used to forward the Ethernet frames across the Service Provider
network, and this much larger physical address space (approx 216) allows for a more
scalable network than the traditional one with VLAN IDs??”where even with the QinQ
scheme, stacking a Service Provider VLAN tag over the customer VLAN tag, only 4094
service instances are supported.
The MAC-in-MAC significantly improves scalability and also provides some security
by separating the customer and Service Provider address space. It also precludes a
MAC address explosion and the need for learning substantially more end-user MAC addresses
in the Service Provider??™s core infrastructure (switches and so on). Minimizing
the number of MAC addresses that need to be learned also reduces the aging out and
relearning of MAC addresses, enhancing end-to-end performance, and in general, making
the network more stable as far as forwarding Ethernet frames is concerned.
Pages:
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256