7-7
QinQ (Provider Bridging)
Introduction
QinQ and Duplicate VIDs. Duplicate VID’s for c-tagged and s-tagged
VLANs (for example, C-VID=100; S-VID=100) are allowed in certain cases and
disallowed in others. Customer-network ports are essentially S-VLAN ports:
they simply read the C-tags in the customer frame to insert them into the
appropriate untagged S-VLAN for that port. Once this double-tagging occurs,
frames are forwarded based on the S-VLAN tag only, while the C-VLAN tag
remains shielded during data transmission. See Figure 7-4 for examples of
allowed configurations.
Figure 7-4. QinQ and Duplicate VIDs: Examples of Allowed Configurations
100
100
Example 1: Duplicate
c-tags are allowed.
100
Svlan Mode
100
100
6U
5U (
Untagged)
5T, 6T
CN (Ports) PN (Ports)
5
6
100
Example 2: Duplicate c-tags
and s-tags are allowed.
100
100
100
101U
100U
100T,
CN PN
100
101
101T
100
Example 3: Remapping
s-tags is NOT allowed.
6T
5T
7T, 8T
PN
PN
7
100
5
100
6
1008
100
Example 4: Duplicate c-tags in
regular and CN ports are allowed.
100
Mixed Mode
101
100U
5U
5T
CN PN
5
100
Example 5: Duplicate c-tags
and s-tags are allowed.
100
100U
CN PN
100
Example 6: Duplicate s-tags
and VIDs in regular ports is
NOT allowed.
100U
PN
PN
Regular (Ports)
101U
200
201
200U
Regular
201U
100T
100
101
100U
Regular
101U
200
100T
100
100
(
Tagged)
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