Stp Rules And Restrictions - Extreme Networks ExtremeWare XOS Guide Manual

Spanning Tree Protocol
Figure 41: Final network configuration
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Compatibility With STP (802.1D)
RSTP interoperates with legacy STP protocols; however, the rapid convergence benefits are lost when
interacting with legacy STP bridges.
Each RSTP bridge contains a port protocol migration state machine to ensure that the ports in the STPD
operate in the correct, configured mode. The state machine is a protocol entity within each bridge
configured to run in 802.1w mode. For example, a compatibility issue occurs if you configure 802.1w
mode and the bridge receives an 802.1D BPDU on a port. The receiving port starts the protocol
migration timer and remains in 802.1D mode until the bridge stops receiving 802.1d BPDUs. Each time
the bridge receives an 802.1D BPDU, the timer restarts. When the port migration timer expires, no more
802.1D BPDUs have been received, and the bridge returns to its configured setting, which is 802.1w
mode.

STP Rules and Restrictions

This section summarizes the rules and restrictions for configuring STP as follows:
The carrier VLAN must span all ports of the STPD.
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The StpdID must be the VLANid of the carrier VLAN; the carrier VLAN cannot be partitioned.
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A default VLAN cannot be partitioned. If a VLAN traverses multiple STPDs, the VLAN must be
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tagged.
An STPD can carry, at most, one VLAN running in PVST+ mode, and its StpdID must be identical
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with that VLANid. In addition, the PVST+ VLAN cannot be partitioned.
The default VLAN of a PVST+ port must be identical with the native VLAN on the PVST+ device
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connected to that port.
If an STPD contains both PVST+ and non-PVST+ ports, that STPD must be enabled. If that STPD is
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disabled, the BPDUs are flooded in the format of the incoming STP port, which may be incompatible
with those of the connected devices.
The 802.1D ports must be untagged; and the EMISTP/PVST+ ports must be tagged in the carrier
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VLAN.
An STPD with multiple VLANs must contain only VLANs that belong to the same virtual router
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instance.
ExtremeWare XOS 11.1 Concepts Guide
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Root Designated
port port
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EX_055h
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