Dell Force10 MXL Blade MXL 10/40GbE Switch IO Module Configuration Guide - Page 413
PVST+ in Multi-vendor Networks, PVST+ Extended System ID, To keep both ports in Forwarding state
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FTOS Behavior: Regarding the bpduguard shutdown-on-violation behavior: 1 If the interface to be shutdown is a port channel, all the member ports are disabled in the hardware. 2 When you add a physical port to a port channel already in Error Disable state, the new member port id also disabled in the hardware. 3 When you remove a physical port from a port channel in Error Disable state, the Error Disabled state is cleared on this physical port (the physical port is enabled in the hardware). 4 You can clear the Error Disabled state with any of the following methods: • Perform a shutdown command on the interface. • Disable the shutdown-on-violation command on the interface (no spanning-tree pvst edge-port [bpduguard | [shutdown-on-violation]]). • Disable spanning tree on the interface (no spanning-tree in INTERFACE mode). • Disabling global spanning tree (no spanning-tree in CONFIGURATION mode). PVST+ in Multi-vendor Networks Some non-Dell Force10 systems that have hybrid ports participating in PVST+, transmit two kinds of BPDUs: an 802.1D BPDU and an untagged PVST+ BPDU. Dell Force10 systems do not expect PVST+ BPDU (tagged or untagged) on an untagged port. If this happens, FTOS places the port in the Error Disable state. This behavior might result in the network not converging. To prevent FTOS from executing this action, use the no spanning-tree pvst err-disable cause invalid-pvst-bpdu command. After you configure this command, if the port receives a PVST+ BPDU, the BPDU is dropped and the port remains operational. PVST+ Extended System ID In Figure 23-6, ports P1 and P2 are untagged members of different VLANs. These ports are untagged because the hub is VLAN unaware. There is no data loop in the above scenario; however, you can employ PVST+ to avoid potential misconfigurations. If you enable PVST+ on the Dell Force10 switch in this network, P1 and P2 receive BPDUs from each other. Ordinarily, the Bridge ID in the frame matches the Root ID, a loop is detected, and the rules of convergence require that P2 move to the Blocking state because it has the lowest port ID. To keep both ports in Forwarding state, use Extend System ID. Extend System ID augments the Bridge ID with a VLAN ID to differentiate BPDUs on each VLAN so that PVST+ does not detect a loop, and both ports can remain in Forwarding state. Per-VLAN Spanning Tree Plus (PVST+) | 411
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