Planet Networking & Communication IGS-6325 Series User Manual page 139

 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
■ 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
Table 4-3-3-1: Ingress / Egress Port with VLAN VID Tag / Untag Table
User's Manual of IGS-6325 series
Income Frame is untagged
Tag is inserted
Frame remain untagged
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