Installation guide

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8 VLAN STACKING
This chapter includes the following sections for configuring VLAN Stacking:
◆ “Configuring IEEE 802.1Q Tunneling” on page 61
◆ “VLAN Stacking Table” on page 62
◆ “VLAN Stacking Settings” on page 63
CONFIGURING IEEE 802.1Q TUNNELING
VLAN Stacking, or IEEE 802.1Q Tunneling (QinQ), is designed for service
providers carrying traffic for multiple customers across their networks.
QinQ tunneling is used to maintain customer-specific VLAN and Layer 2
protocol configurations even when different customers use the same
internal VLAN IDs. This is accomplished by inserting Service Provider VLAN
(S-VLAN) tags into the customer’s frames when they enter the service
provider’s network, and then stripping the tags when the frames leave the
network.
A service provider’s customers may have specific requirements for their
internal VLAN IDs and number of VLANs supported. VLAN ranges required
by different customers in the same service-provider network might easily
overlap, and traffic passing through the infrastructure might be mixed.
Assigning a unique range of VLAN IDs to each customer would restrict
customer configurations, require intensive processing of VLAN mapping
tables, and could easily exceed the maximum VLAN limit of 4096.
QinQ tunneling uses a single Service Provider VLAN (S-VLAN) for
customers who have multiple VLANs. Customer VLAN IDs are preserved
and traffic from different customers is segregated within the service
provider’s network even when they use the same customer-specific VLAN
IDs. QinQ tunneling expands VLAN space by using a VLAN-in-VLAN
hierarchy, preserving the customer’s original tagged packets, and adding
S-VLAN tags to each frame (also called double tagging).
A port configured to support QinQ tunneling must be set to tunnel port
mode. The Service Provider VLAN (S-VLAN) ID for the specific customer
must be assigned to the QinQ tunnel access port on the edge switch where
the customer traffic enters the service provider’s network. Each customer
requires a separate S-VLAN, but this VLAN supports all of the customer's
internal VLANs. The QinQ tunnel uplink port that passes traffic from the
edge switch into the service provider’s metro network must also be added
to this S-VLAN. The uplink port can be added to multiple S-VLANs to carry
inbound traffic for different customers onto the service provider’s network.