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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