Dell Networking 2048, Reference Manual

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VLAN Commands
The Dell Networking switching component can be configured to enable the
port in double-VLAN (DVLAN) mode. In this mode switch looks for 12th,
13th, 16th, and 17th bytes for the tag status in the incoming frame. The outer
tag (S-TAG) TPID is identified with the 12th and 13th bytes values. The
inner tag (C-TAG) TPID is identified with 16th and 17th bytes values. These
two TPID values can be different or the same. VLAN normalization, source
MAC learning, and forwarding are based on the S-TAG value in a received
frame.
Dell Networking supports configuring one outer VLAN TPID value per
switch. The global default TPID is 0x88A8, which indicates a Virtual
Metropolitan Area Network (VMAN).
Independent VLAN Learning
Independent VLAN Learning (IVL) allows unicast address-to-port mappings
to be created based on a MAC Address in conjunction with a VLAN ID.
This arrangement associates the MAC Address only with the VLAN on which
the frame was received. Therefore, frames are forwarded based on their
unicast destination address as well as their VLAN membership. This
configuration affords multiple occurrences of an address in the forwarding
database. Each address associates with a unique VLAN. Care must be taken
in the administration of networks, as multiple instances of a MAC address,
each on a different VLAN, can quickly eat up address entries.
Each VLAN is associated with its own forwarding database. Hence the
number of forwarding databases equals the number of VLANs supported.
The MAC address stored is supplemented by a 2-byte VLAN ID. The first 2
bytes of a forwarding database entry contain the VLAN ID associated, and the
next 6 bytes contain the MAC address. There is a one-to-one relationship
between VLAN ID and FID (forwarding database ID).
Protocol Based VLANs
The main purpose of Protocol-based VLANs (PBVLANs) is to selectively
process packets based on their upper-layer protocol by setting up protocol-
based filters. Packets are bridged through user-specified ports based on their
protocol.
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