Cisco 500 series Administration Manual page 205

VLAN Management
VLANs
Cisco 500 Series Stackable Managed Switch Administration Guide
The IP router might be a traditional router, where each of its interfaces connects to
only one VLAN. Traffic to and from a traditional IP router must be VLAN untagged.
The IP router can be a VLAN-aware router, where each of its interfaces can
connect to one or more VLANs. Traffic to and from a VLAN-aware IP router can be
VLAN tagged or untagged.
Adjacent VLAN-aware devices exchange VLAN information with each other by
using Generic VLAN Registration Protocol (GVRP). As a result, VLAN information is
propagated through a bridged network.
VLANs on a device can be created statically or dynamically, based on the GVRP
information exchanged by devices. A VLAN can be static or dynamic (from GVRP),
but not both. For more information about GVRP, refer to the GVRP Settings section.
Some VLANs can have additional roles, including:
• Voice VLAN: For more information refer to the Voice VLAN section.
• Guest VLAN: Set in the Edit VLAN Authentication page.
• Default VLAN: For more information refer to the Configuring Default VLAN
Settings section.
• Management VLAN (in Layer 2-system-mode systems): For more
information refer to the Layer 2 IP Addressing section.
QinQ
QinQ provides isolation between service provider networks and customers'
networks. The switch is a provider bridge that supports port-based c-tagged
service interface.
With QinQ, the switch adds an ID tag known as Service Tag (S-tag) to forward
traffic over the network. The S-tag is used to segregate traffic between various
customers, while preserving the customer VLAN tags.
Customer traffic is encapsulated with an S-tag with TPID 0x8100, regardless of
whether it was originally c-tagged or untagged. The S-tag allows this traffic to be
treated as an aggregate within a provider bridge network, where the bridging is
based on the S-tag VID (S-VID) only.
The S-Tag is preserved while traffic is forwarded through the network service
provider's infrastructure, and is later removed by an egress device.
An additional benefit of QinQ is that there is no need to configure customers' edge
devices.
QinQ is enabled in the VLAN Management > Interface Settings page.
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