Editing Spanning Tree Protocol (section)

=== Proprietary standards ===
Before the IEEE published a Spanning Tree Protocol standard for VLANs, a number of vendors who sold VLAN-capable switches developed their own Spanning Tree Protocol versions that were VLAN capable. [[Cisco]] developed, implemented and published the {{anchor|PVST}}'''Per-VLAN Spanning Tree''' ('''PVST''') [[proprietary protocol]] using its own proprietary [[Cisco Inter-Switch Link|Inter-Switch Link]] (ISL) for VLAN [[Encapsulation (networking)|encapsulation]], and PVST+ which uses [[802.1Q]] VLAN encapsulation. Both standards implement a separate spanning tree for every VLAN. Cisco switches now commonly implement PVST+ and can only implement Spanning Trees for VLANs if the other switches in the LAN implement the same VLAN STP protocol. HP provides PVST and PVST+ compatibility in some of its network switches.<ref name="Solomon"/> Some devices from [[Force10 Networks]], [[Alcatel-Lucent]], [[Extreme Networks]], [[Avaya]], [[Brocade Communications Systems]] and [[BLADE Network Technologies]] support PVST+.<ref>{{cite web
|url=https://www.force10networks.com/CSPortal20/TechTips/0050B_HowDoIConfigureSpanningTree.aspx|title=Technical Documentation |publisher=[[Force10]]|access-date=2011-01-25}}</ref><ref>{{cite web |url=http://www.extremenetworks.com/libraries/products/DSExtXOS_1030.pdf |archive-url=https://web.archive.org/web/20061126120914/http://www.extremenetworks.com/libraries/products/DSExtXOS_1030.pdf |archive-date=2006-11-26 |url-status=live|title=ExtremeXOS Operating System, Version 12.5|publisher=[[Extreme Networks]] | year=2010| access-date=2011-01-25}}</ref><ref>{{cite web |url=http://www.bladenetwork.net/userfiles/file/PDFs/WP_PVST_SpanningTree_Cisco.pdf |archive-url=https://web.archive.org/web/20100612021303/http://bladenetwork.net/userfiles/file/PDFs/WP_PVST_SpanningTree_Cisco.pdf |archive-date=2010-06-12 |url-status=live |title=BLADE PVST+ Interoperability with Cisco |year=2006 |access-date=2011-01-25}}</ref> Extreme Networks does so with two limitations: Lack of support on ports where the VLAN is untagged/native, and also on the VLAN with ID 1. PVST+ can tunnel across an MSTP Region.<ref>{{cite web|url=http://www.cisco.com/en/US/docs/ios/12_1t/12_1t3/feature/guide/dtbridge.html#wp1020686 |title=Bridging Between IEEE 802.1Q VLANs |publisher=Cisco Systems|access-date=2011-01-25}}</ref>

The switch vendor [[Juniper Networks]] in turn developed and implemented its VLAN Spanning Tree Protocol (VSTP) to provide compatibility with Cisco's PVST, so that the switches from both vendors can be included in one LAN.<ref name="Solomon"/> The VSTP protocol is only supported by the EX and MX Series from Juniper Networks. There are two restrictions to the compatibility of VSTP:
#VSTP supports only 253 different spanning-tree topologies. If there are more than 253 VLANs, it is recommended to configure RSTP in addition to VSTP, and VLANs beyond 253 will be handled by RSTP.
#[[MVRP]] does not support VSTP. If this protocol is in use, VLAN membership for trunk interfaces must be statically configured.<ref>{{cite web |url=http://www.juniper.net/techpubs/en_US/junos10.0/topics/concept/bridging-mvrp-ex-series.html |title=Juniper Networks :: Technical Documentation :: Understanding Multiple VLAN Registration Protocol (MVRP) on EX Series Switches |website=www.juniper.net |url-status=dead |archive-url=https://web.archive.org/web/20120407024355/http://www.juniper.net/techpubs/en_US/junos10.0/topics/concept/bridging-mvrp-ex-series.html |archive-date=2012-04-07}}</ref>

By default, VSTP uses the RSTP protocol as its core spanning-tree protocol, but usage of STP can be forced if the network includes old bridges.<ref>{{Cite web|url=https://www.juniper.net/techpubs/en_US/junos9.4/topics/concept/spanning-trees-ex-series-vstp-understanding.html|title=Juniper Networks :: Technical Documentation :: Understanding VSTP for EX-series Switches}}</ref> More information about configuring VSTP on Juniper Networks switches was published in the official documentation.<ref>[https://www.juniper.net/techpubs/en_US/junos14.1/topics/concept/spanning-trees-ex-series-vstp-understanding.html Understanding VSTP]</ref>

Cisco also published a proprietary version of Rapid Spanning Tree Protocol. It creates a spanning tree for each VLAN, just like PVST. Cisco refers to this as {{anchor|RPVST}}'''Rapid Per-VLAN Spanning Tree''' ('''RPVST''').