Configuration Guide User guide

1158 FastIron Configuration Guide
53-1002494-02
PVST/PVST+ compatibility
IEEE 802.1Q and PVST regions cannot interoperate directly but can interoperate indirectly through
PVST+ regions. PVST BPDUs are tunnelled through 802.1Q regions, while PVST BPDUs for VLAN 1
(the IEEE 802.1Q VLAN) are processed by PVST+ regions. Figure 153 shows the interaction of IEEE
802.1Q, PVST, and PVST+ regions.
FIGURE 153 Interaction of IEEE 802.1Q, PVST, and PVST+ regions
VLAN tags and dual mode
The dual-mode feature enables a port to send and receive both tagged and untagged frames.
When the dual-mode feature is enabled on a port, 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 Port Native VLAN.
The dual-mode feature must be enabled on a Brocade port in order to interoperate with another
vendor device. 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 untagged frames on VLAN 1. On
Brocade switches, by default, the Port Native VLAN is the same as the Default VLAN, which is VLAN
1. Thus, to support IEEE 802.1Q in a typical configuration, a port must be able to send and receive
untagged frames for VLAN 1 and tagged frames for the other VLANs, and interoperate with other
vendor devices 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 the untagged (native) VLAN is also changed on the interoperating
vendor side to match that on the Brocade side.
PVST+Region IEEE 802.1Q Region
PVST+Region
PVST Region
PVST BPDUs
(over ISL trunks)
PVST BPDUs
(over ISL trunks)
Do not
connect
dual mode
port
dual mode
port
802.1D BPDUs
802.1D BPDUs
PVST BPDUs tunneled through
the IEEE 802.1Q region