Planet GS-5220 Series User Manual page 193

User's Manual of GS-5220 LCD Series
The Managed Switch supports multiple VLAN tags and can therefore be used in MAN applications as a provider
bridge, aggregating traffic from numerous independent customer LANs into the MAN (Metro Access Network)
space. One of the purposes of the provider bridge is to recognize and use VLAN tags so that the VLANs in the
MAN space can be used independent of the customers' VLANs. This is accomplished by adding a VLAN tag with a
MAN-related VID for frames entering the MAN. When leaving the MAN, the tag is stripped and the original VLAN
tag with the customer-related VID is again available.
This provides a tunneling mechanism to connect remote costumer VLANs through a common MAN space
without interfering with the VLAN tags. All tags use EtherType 0x8100 or 0x88A8, where 0x8100 is used for
customer tags and 0x88A8 are used for service provider tags.
In cases where a given service VLAN only has two member ports on the switch, the learning can be disabled for
the particular VLAN and can therefore rely on flooding as the forwarding mechanism between the two ports.
This way, the MAC table requirements is reduced.
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