Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 322)

FIGURE 69 Port Native VLAN 2 for Untagged BPDUs
To implement this configuration, enter the following commands.
Commands on the Brocade Device
device(config)#default-vlan-id 4000
device(config)#vlan 1
device(config-vlan-1)#tagged ethernet 1/1
device(config-vlan-1)#exit
device(config)#vlan 2
device(config-vlan-2)#tagged ethernet 1/1
device(config-vlan-2)#exit
device(config)#interface ethernet 1/1
device(config-if-1/1)#dual-mode 2
device(config-if-1/1)#pvst-mode
device(config-if-1/1)#exit
These commands change the default VLAN ID, configure port 1/1 as a tagged member of VLANs 1
and 2, and enable the dual-mode feature and PVST+ support on port 1/1. Since VLAN 1 is tagged in
this configuration, the default VLAN ID must be changed from VLAN 1 to another VLAN ID. Changing
the default VLAN ID from 1 allows the port to process tagged frames for VLAN 1. VLAN 2 is specified
with the dual-mode command, which makes VLAN 2 the port Port Native VLAN. As a result, the port
processes untagged frames and untagged PVST BPDUs on VLAN 2.
NOTE
Although VLAN 2 becomes the port untagged VLAN, the CLI still requires that you add the port to the
VLAN as a tagged port, since the port is a member of more than one VLAN.
Port 1/1 will process BPDUs as follows:
• Process IEEE 802.1Q BPDUs for VLAN 1.
• Process untagged PVST BPDUs for VLAN 2.
• Drop tagged PVST BPDUs for VLAN 1.
Note that when VLAN 1 is not the default VLAN, the ports must have the dual-mode feature enabled in
order to process IEEE 802.1Q BPDUs.
For example, the following configuration is incorrect.
device(config)#default-vlan-id 1000
device(config)#vlan 1
device(config-vlan-1)#tagged ethernet 1/1 to 1/2
device(config-vlan-1)#exit
device(config)#interface ethernet 1/1
device(config-if-1/1)#pvst-mode
device(config-if-1/1)#exit
device(config)#interface ethernet 1/2
device(config-if-1/2)#pvst-mode
device(config-if-1/2)#exit
In the configuration above, all PVST BPDUs associated with VLAN 1 would be discarded. Since IEEE
BPDUs associated with VLAN 1 are untagged, they are discarded because the ports in VLAN 1 are
tagged. Effectively, the BPDUs are never processed by the Spanning Tree Protocol. STP assumes
Spanning Tree Protocol
322 FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide
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