Dell Force10 S25N-S50N FTOS Configuration Guide FTOS 8.4.2.7 E-Series TeraScal - Page 951

46 Service Provider Bridging c e s Service Provider Bridging is supported on platforms: This chapter contains the following major sections: • VLAN Stacking on page 951 • VLAN Stacking Packet Drop Precedence on page 962 • Dynamic Mode CoS for VLAN Stacking on page 965 • Layer 2 Protocol Tunneling on page 967 • Provider Backbone Bridging on page 971 VLAN Stacking c e s VLAN Stacking is supported on platforms: e VLAN Stacking is supported on E-Series ExaScale x with FTOS 8.2.1.0. and later. VLAN Stacking, also called Q-in-Q, is defined in IEEE 802.1ad-Provider Bridges, which is an amendment to IEEE 802.1Q-Virtual Bridged Local Area Networks. It enables service providers to use 802.1Q architecture to offer separate VLANs to customers with no coordination between customers, and minimal coordination between customers and the provider. Using only 802.1Q VLAN tagging all customers would have to use unique VLAN IDs to ensure that traffic is segregated, and customers and the service provider would have to coordinate to ensure that traffic mapped correctly across the provider network. Even under ideal conditions, customers and the provider would still share the 4094 available VLANs. Instead, 802.1ad allows service providers to add their own VLAN tag to frames traversing the provider network. The provider can then differentiate customers even if they use the same VLAN ID, and providers can map multiple customers to a single VLAN to overcome the 4094 VLAN limitation. Forwarding decisions in the provider network are based on the provider VLAN tag only, so the provider can map traffic through the core independently; the customer and provider need only coordinate at the provider edge. Service Provider Bridging | 951