Provider networks
handle traffic from a large number of customers. It is important that one
customer’s traffic is isolated from the other customer’s traffic.
IEEE 802.1ad enables
the service providers to use the architecture and protocols of IEEE 802.1Q to
offer separate LANs, bridged local area networks, or virtual bridged local area
networks to a number of customers, with minimal cooperation or no cooperation
between each customer and the service provider.
IEEE 802.1ad
implements standard protocols for double tagging of data. The data traffic
coming from the customer side are double tagged in the provider network where
the inner tag is the customer-tag (C-tag) and the outer tag is the provider-tag
(S-tag). The control packets are tunneled by changing the destination MAC
address in the provider network.
A service provider's
Layer 2 network transports the subscriber's Layer 2 protocols transparently.
Provider Bridge allows the service provider switches to transparently carry
customer Layer 2 control frames, such as spanning tree Bridge Protocol Data
Units (BPDUs) or Cisco proprietary protocol frames such as Cisco Discovery
Protocol (CDP) without mixing the service provider's own traffic and with other
customer traffic in the service provider's network. A provider bridge is just
like a standard 802.1Q bridge, but it imposes a set of requirements, defined by
IEEE 802.1ad standards, on a port in a provider bridge which interfaces to
customer. This port is a UNI Port. 802.1ad Provider Bridge thus achieves the
same functionality as being addressed with L2PT and QinQ.
When Connectivity
Fault Management (CFM) is configured on 802.1ad interfaces, all CFM, Link
Ethernet Operations, Administration, and Maintenance (OAM), Enhanced Local
Management Interface (ELMI) or Y.1731 performance monitoring packets have their
own peer or data rules depending on the type of 802.1ad port configured.
Feedback