Chapter 11 Spanning Tree Protocol
11.1.3 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.
Table 26 STP Port States
PORT | DESCRIPTION | |
STATE | ||
| ||
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. |
11.1.4 Multiple STP
Multiple Spanning Tree Protocol (IEEE 802.1s) is backwards 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.
•
11.1.4.1MSTP Network Example
The following figure shows a network example where two VLANs are configured on the two switches. If the switches are using STP or RSTP, the link for VLAN 2 will be
| 107 |
|
|