TECHNOLOGY

Ethernet

Q-in-Q

Q-in-Q, also known as stacked VLAN, supports the encapsulation of IEEE802.1Q VLAN tag (CY-LAN) within an outer layer of 802.1Q tag (SVLAN). In an Ethernet-based switched network, only the first tag is used by the Ethernet switches — for making forwarding decisions. As a result, using Q-in-Q allows service providers to support customers with multiple VLANs through the use of one single SVLAN.

This simplifies management of the VLAN identifiers in the provider’s Ethernet-based backbone. Also, because only SVLAN is used for forwarding decisions, Q-in-Q allows segregation of customer traffic by assigning a unique SVLAN for each customer. The VLAN feature is supported on the HSX 6000 for L2 Ethernet services as well as over tagged-mode Ethernet Pseudowire.

The Ethernet Type field that identifies the presence of an SVLAN is user configurable per Ethernet interface. The HSX 6000 supports simultaneous use of 802.1q VLAN and SVLAN, although any push, pop, or swap tag operations can only be applied for the outermost tag.

In the HSX 6000, a range of VLANs can be specified at the time a cross connection is created. This allows for creating trunks that carry more than one VLAN circuit, analogous to virtual pipes carrying a set of VC’s in ATM. As shown in the list below, these trunks can be SVLAN based, ATM/FR based, and raw or tagged Pseudowire based.

VLAN Range to SVLAN Trunk

Able to map a range of VLANs (such as 100-4000, 0-4093) to a carrier VLAN tagged flow.

VLAN Range to Pseudowire (raw and tagged)

Able to receive customer equipment VLAN and forward it as is on the raw-Pseudowire. In the case of tagged Pseudowire, a configured tag is PUSHED and the provider equipment will POP the outer tag.

VLAN Range to ATM/FR

VLAN range for ATM and FR is supported in bridged mode only and the VLAN -tag is sent as is.

NOTE: ATM/FR interworking is restricted to bridged mode, as the Ethernet header cannot be completely removed.