340 BigIron RX Series Configuration Guide53-1001986-01PVST/PVST+ compatibility12If you want to use tagged frames on VLAN 1, you can change the default VLAN ID to an ID otherthan 1. You also can specify the VLAN on which you want the port to send and receive untaggedframes (the native VLAN). The Port Native VLAN ID does not need to be the same as the defaultVLAN.NOTESupport for the IEEE 802.1Q spanning tree always uses VLAN 1, regardless of whether the devicesare configured to use tagged or untagged frames on the VLAN.Enabling PVST+ supportPVST+ support is automatically enabled when the port receives a PVST BPDU. You can manuallyenable the support at any time or disable the support if desired.If you want a tagged port to also support IEEE 802.1Q BPDUs, you need to enable the dual-modefeature on the port. The dual-mode feature is disabled by default and must be enabled manually.A port that is in PVST+ compatibility mode due to auto-detection reverts to the default MSTP modewhen one of the following events occurs:• The link is disconnected or broken• The link is administratively disabled• The link is disabled by interaction with the link-keepalive protocolThis allows a port that was originally interoperating with PVST+ to revert to multiple spanning treewhen connected to a device.Enabling PVST+ support manuallyTo immediately enable PVST+ support on a port, enter commands such as the following.BigIron RX(config)# interface ethernet 1/1BigIron RX(config-if-e1000-1/1)# pvst-modeSyntax: [no] pvst-modeNOTEIf you disable PVST+ support, the software still automatically enables PVST+ support if the portreceives a BPDU with PVST+ format.Displaying PVST+ support informationTo display PVST+ information for ports on a device, enter the following command at any level of theCLI.
