Chapter 3: Spanning Tree Protocol
When you remove a port from a VLAN that belongs to an STG, that port is removed from the STG. However, if that port belongs to another VLAN in the same STG, the port remains in the STG.
As an example, assume that port 1 belongs to VLAN 2, and VLAN 2 belongs to STG 2. When you remove port 1 from VLAN 2, port 1 is also removed from STG 2. The port moves to the default VLAN 1.
However, if port 1 belongs to both VLAN 1 and VLAN 2 and both VLANs belong to STG 1, removing port 1 from VLAN 2 does not remove port 1 from STG 1 because VLAN 1 is still a member of STG 1.
An STG cannot be deleted, only disabled. If you disable the STG while it still contains VLAN members, Spanning Tree will be off on all ports belonging to that VLAN.
The relationship between port, trunk groups, VLANs, and spanning trees is shown in Table 9.
Rapid Spanning Tree Protocol
Rapid Spanning Tree Protocol (RSTP) provides rapid convergence of the spanning tree and provides for fast
RSTP parameters are configured in Spanning Tree Group 1. Spanning Tree Groups 2 through 128 do not apply to RSTP. There are new STP parameters to support RSTP, and some values to existing parameters are different.
RSTP is compatible with devices that run 802.1D (1998) Spanning Tree Protocol. If the switch detects 802.1D (1998) BPDUs, it responds with 802.1D
Port State Changes
The port state controls the forwarding and learning processes of Spanning Tree. In RSTP, the port state has been consolidated to the following: discarding, learning, and forwarding. Table 10 compares the port states between 802.1D (1998) Spanning Tree and 802.1D (2004) Rapid Spanning Trees.
Table 10: RSTP vs. STP Port States
Operational Status | STP Port State | RSTP Port State |
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Enabled | Blocking | Discarding |
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Enabled | Listening | Discarding |
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Enabled | Learning | Learning |
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Enabled | Forwarding | Forwarding |
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Disabled | Disabled | Discarding |
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Rapid Spanning Tree Protocol 35
