Multiple Instance
802.1s Multiple Spanning Tree Protocol (MSTP)
| 802.1s Multiple Spanning Tree Protocol |
| (MSTP) |
| The 802.1D and 802.1w spanning tree protocols operate without regard to a |
| network’s VLAN configuration, and maintain one common spanning tree |
| throughout a bridged network. Thus, these protocols map one |
| logical topology on a given physical topology. The 802.1s Multiple Spanning |
| Tree protocol (MSTP) uses VLANs to create multiple spanning trees in a |
| network, which significantly improves network resource utilization while |
| maintaining a |
| While the |
| comes the network utilization problems inherent in using STP or RSTP, using |
| a |
| MSTP on the switches covered in this guide complies with the IEEE 802.1s |
| standard, and extends STP and RSTP functionality to map multiple indepen- |
| dent spanning tree instances onto a physical topology. With MSTP, each |
| spanning tree instance can include one or more VLANs and applies a separate, |
| |
| VLANs, it may be dynamically blocked in one spanning tree instance, but |
| forwarding in another instance. This achieves |
| work while keeping the switch’s CPU load at a moderate level (by aggregating |
| multiple VLANs in a single spanning tree instance). MSTP provides fault |
| tolerance through rapid, automatic reconfiguration if there is a failure in a |
| network’s physical topology. |
| With |
| taining multiple spanning tree instances. This requires the configuration of a |
| number of |
| You can just enable MSTP on an |
| instance is created automatically. This instance always exists by default when |
| spanning tree is enabled, and is the spanning tree instance that communicates |
| with STP and RSTP environments. The MSTP configuration commands oper- |
| ate exactly like RSTP commands and MSTP is |
| |
|
|
C a u t i o n | Spanning tree interprets a switch mesh as a single link. Because the switch |
| automatically gives faster links a higher priority, the default MSTP parameter |
| settings are usually adequate for spanning tree operation. Also, because |
| incorrect MSTP settings can adversely affect network performance, you |
| should not change the MSTP settings from their default values unless you have |
| a strong understanding of how spanning tree operates. |