Multiple Spanning Tree Protocol: Difference between revisions

Revision as of 17:18, 13 January 2018

Revision as of 09:14, 10 May 2018

Line 8:

It was originally defined in [[Institute of Electrical and Electronics Engineers|IEEE]] 802.1s as an amendment to [[IEEE 802.1Q|802.1Q]], 1998 edition and later merged into IEEE 802.1Q-2005 Standard, clearly defines an extension or an evolution of [[Radia Perlman]]'s Spanning Tree Protocol (STP) and the [[Spanning Tree Protocol#Rapid Spanning Tree Protocol|Rapid Spanning Tree Protocol]] (RSTP). It has some similarities with [[Cisco Systems]]' Multiple Instances Spanning Tree Protocol (MISTP), but there are some differences.

The original STP and RSTP work on the physical link level, preventing bridge loops when redundant paths are present. However, when a LAN is virtualized using VLAN trunking, each physical link represents multiple logical connections. Blocking a physical link blocks all its logical links and forces all traffic through the remaining physical links within the [[spanning tree]]. Redundant links cannot be utilized at all. Moreover, without careful network design, seemingly redundant links on the physical level may be used to connect ''different'' VLANs and blocking any of them may disconnect one or more VLANs, causing ''bad paths''.

If there is only one VLAN in the network, single (traditional) STP/RSTP will work appropriately but if the network contains more than one VLAN, the logical network configured by single STP/RSTP wouldn't work as efficiently as it is supposed to, even letting some errors (loops, bad paths…) to appear. Instead, it is possible to make better use of the alternate paths available by using an alternate [[spanning tree]] for different VLANs or groups of VLANs, here is where the necessity of hammering away a new extension of RSTP philosophy into multiple trees organized by VLANs' groups came up.

Instead, MSTP provides a potentially better utilization of alternate paths by enabling the use of alternate spanning trees for different VLANs or groups of VLANs.

== Main Entities ==