PVST+和RSTP混合使用

gdxnfx

有四台交换机s1--s2---s3---s4---s1 组成一个环网。
其中s1和s2运行PVST+， s3和s4运行RSTP。其中s1为根桥.
我怀疑PVST+和RSTP是否可以混合使用？
有没有实际使用过的朋友？
https://supportwiki.cisco.com/Vi ... ith_redundant_links

gdxnfx

当RSTP端口接收到802。1D包的时候，会怎么处理？

gdxnfx

好像可以混合使用.有机会测试一下。
Background Information
802.1D Spanning Tree Protocol (STP) has a drawback of slow convergence. Cisco Catalyst switches support three types of STPs, which are PVST+, rapid-PVST+ and MST. PVST+ is based on IEEE802.1D standard and includes Cisco proprietary extensions such as BackboneFast, UplinkFast, and PortFast. Rapid-PVST+ is based on IEEE 802.1w standard and has a faster convergence than 802.1D. RSTP (IEEE 802.1w) natively includes most of the Cisco proprietary enhancements to the 802.1D Spanning Tree, such as BackboneFast and UplinkFast. Rapid-PVST+ has these unique features:

Uses Bridge Protocol Data Unit (BPDU) version 2 which is backward compatible with the 802.1D STP, which uses BPDU version 0.

All the switches generate BPDUs and send out on all the ports every 2 seconds, whereas in 802.1D STP only the root bridge sends the configuration BPDUs.

Port Roles—Root port, designated port, alternate port and backup port.

Port States—Discarding, Learning, and Forwarding.

Port Types—Edge Port (PortFast), Point-to-Point and Shared port.

Rapid-PVST uses RSTP to provide faster convergence. When any RSTP port receives legacy 802.1D BPDU, it falls back to legacy STP and the inherent fast convergence benefits of 802.1w are lost when it interacts with legacy bridges.

gdxnfx

没有办法才混用的，现在是过渡时期，到最后肯定会使用相同的生成树模式。

经测试，在Cisco Nexus 上运行RSTP ,在cisco 6509上运行PVST+，可以正常的运行。

从生成树的状态来看，运行RSTP的Nexus与运行PVST+没有什么区别，运行RSTP的Nexus能够处理PVST+ BPDU数据包。

至于其他厂家的RSTP能否跟Cisco的PVST+混合应用就不清楚了。

gdxnfx

Replied by: ftallet - Technical Leader, CISCO SYSTEMS, CCIE - Aug 25, 2009, 6:28am PST


The interaction STP/RSTP is specified in the standard, it is not specific to Cisco (even if here, PVST modes are cisco proprietary). Basically, STP bridges drop RSTP BPDUs. As a result, they send BPDUs to their RSTP neighbors. An RSTP bridge that receives an STP BPDU know that it's connected to a legacy device and start sending STP BPDUs itself.
This mechanism will happen on a per-vlan basis with Cisco PVST/Rapid-PVST.
Regards,
Francois

gdxnfx

华为的RSTP估计是标准的802。1W，cisco 的RSTP是基于802.1w的Rapid-PVST .
能不能正常运行，还真要实际测试

gdxnfx

原帖由 ssffzz1 于 2009-8-26 16:05 发表
RSTP===802.3W

PVST+ CISCO完全私有。

RSTP = 802.1w


In 1998, the IEEE with document 802.1w introduced an evolution of the

Spanning Tree Protocol: Rapid Spanning Tree Protocol (RSTP), which provides

for faster spanning tree convergence after a topology change. Standard IEEE

802.1D-2004 now incorporates RSTP and obsoletes STP. While STP can take 30

to 50 seconds to respond to a topology change, RSTP is typically able to

respond to changes within a second.[7][8]

PVST+ is based on IEEE802.1D standard and includes Cisco proprietary

extensions such as BackboneFast, UplinkFast, and PortFast.


http://www.cisco.com/en/US/tech/ ... _white_paper09186a0

080094cfa.shtml
http://en.wikipedia.org/wiki/Spanning_tree_protocol#Rapid_Per-

VLAN_Spanning_Tree_.28R-PVST.29

gdxnfx

原帖由 ssffzz1 于 2009-8-24 20:47 发表
PVST+的PID字段，0X010B
此字段是SNAP封装的TYPE字段，以太网要求小于0X600,用于区分TYPE和LENGTH,此值小于0x600会导致不支持PVST+的设备识别错误而丢弃报文，因此PVST+的BPDU无法透传，PVST+无法正常工作。
...

有没有相关的文档 ?

802.1d bpdu :
An IEEE 802.1d Bpdu has the following format:

protocol id:   0000 IEEE 802.1d
version id:    00
bpdu type:     00 config bpdu, 80 tcn bpdu
bit field:     1 byte
  1 : topology change flag
  2 : unused    0
  3 : unused    0
  4 : unused    0
  5 : unused    0
  6 : unused    0
  7 : unused    0
  8 : topology change ack
root priority    2 bytes
root id:         6 bytes
root path cost:  4 bytes
bridge priority: 2 bytes
bridge id:       6 bytes
port id:         2 bytes
message age:     2 bytes in 1/256 secs
max age:         2 bytes in 1/256 secs
hello time:      2 bytes in 1/256 secs
forward delay:   2 bytes in 1/256 secs



Few changes have been introduced by RSTP to the BPDU format. Only two flags, Topology Change (TC) and TC Acknowledgment (TCA), are defined in 802.1D. However, RSTP now uses all six bits of the flag byte that remain in order to perform:

Encode the role and state of the port that originates the BPDU

Handle the proposal/agreement mechanism

Another important change is that the RSTP BPDU is now of type 2, version 2. The implication is that legacy bridges must drop this new BPDU. This property makes it easy for a 802.1w bridge to detect legacy bridges connected to it.