Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 381)

Multi-Service IronWare Switching Configuration Guide 351
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PVST or PVST+ compatibility
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FIGURE 63 Interaction of IEEE 802.1Q, PVST, and PVST+ regions
VLAN Tags and dual mode
The dual-mode feature enables the port to send and receive both tagged and untagged frames on
a port. When the dual-mode feature is enabled, the port is an untagged member of one of its
VLANs and is at the same time a tagged member of all its other VLANs. The untagged frames are
supported on the port’s Port Native VLAN.
To interoperate with other vendors, the dual-mode feature must be enabled on the port. Some
vendors use VLAN 1 by default to support the IEEE 802.1Q based standard spanning tree protocols
such as 802.1d and 802.1w for sending the untagged frames on VLAN 1. On Brocade devices by
default, the Port Native VLAN is the same as the device’s Default VLAN1, which by default is VLAN
1. Thus, to support IEEE 802.1Q in a typical configuration, the port must be able to send and
receive untagged frames for VLAN 1 and tagged frames for the other VLANs and interoperate with
the vendors also using VLAN 1. If you want to use tagged frames on VLAN 1, you can change the
default VLAN ID to an ID other than 1. You also can specify the VLAN on which you want the port to
send and receive untagged frames (the Port Native VLAN). The Port Native VLAN ID does not need
to be the same as the Default VLAN. Make sure that untagged (Native) VLAN is also changed on the
interoperating vendor side to match with that on the Brocade side.
To support the IEEE 802.1Q with non-standard proprietary protocols such as PVST and PVST+, a
port must always send and receive untagged frames on VLAN 1 on both sides. In that case, enable
the dual-mode 1 feature to allow untagged BPDUs on VLAN 1and use Native VLAN 1 on the
interoperating vendor side. You should not use VLAN 1 for tagged frames in this case.
NOTE
Support for the IEEE 802.1Q spanning tree always uses VLAN 1, regardless of whether the Brocade
devices are configured to use tagged or untagged frames on the VLAN.