User’s Manual of IGS-10020MT
123
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
4095.
The Industrial 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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