Chapter 13 Spanning Tree Protocol
XGS1930 Series User’s Guide
131
STP Port States
STP assigns five port states to eliminate packet looping. A bridge port is not allowed to go directly from
blocking state to forwarding state so as to eliminate transient loops.
Multiple STP
Multiple Spanning Tree Protocol (IEEE 802.1s) is backward compatible with STP/RSTP and addresses the
limitations of existing spanning tree protocols (STP and RSTP) in networks to include the following
features:
• One Common and Internal Spanning Tree (CIST) that represents the entire network’s connectivity.
• Grouping of multiple bridges (or switching devices) into regions that appear as one single bridge on
the network.
• A VLAN can be mapped to a specific Multiple Spanning Tree Instance (MSTI). MSTI allows multiple
VLANs to use the same spanning tree.
• Load-balancing is possible as traffic from different VLANs can use distinct paths in a region.
13.2 Spanning Tree Protocol Status Screen
The Spanning Tree Protocol status screen changes depending on what standard you choose to
implement on your network. Click Advanced Application > Spanning Tree Protocol to see the screen as
shown.
Figure 97 Advanced Application > Spanning Tree Protocol
Table 58 STP Port States
PORT STATE DESCRIPTION
Disabled STP is disabled (default).
Blocking Only configuration and management BPDUs are received and processed.
Listening All BPDUs are received and processed.
Note: The listening state does not exist in RSTP.
Learning All BPDUs are received and processed. Information frames are submitted to the learning process
but not forwarded.
Forwarding All BPDUs are received and processed. All information frames are received and forwarded.
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