Planet GS-5220 Series User Manual page 192

• Untagged: Ports with untagging enabled will strip the 802.1Q tag from all packets that flow
into those ports. If the packet doesn't have an 802.1Q VLAN tag, the port will not
alter the packet. Thus, all packets received by and forwarded by an untagging port
will have no 802.1Q VLAN information. (Remember that the PVID is only used
internally within the Switch). Untagging is used to send packets from an
802.1Q-compliant network device to a non-compliant network device.
Frame Income
Frame Leave
Leave port is tagged
Leave port is untagged
Table 4-6-1: Ingress / Egress Port with VLAN VID Tag / Untag Table
■ IEEE 802.1Q Tunneling (Q-in-Q)
IEEE 802.1Q Tunneling (Q-in-Q) is designed for service providers carrying traffic for multiple customers across
their networks. Q-in-Q 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 (SPVLAN) 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.
Income Frame is tagged
Frame remains tagged
Tag is removed
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User's Manual of GS-5220 LCD Series
Income Frame is untagged
Tag is inserted
Frame remain untagged