RE: PVST vs PVST+

From: Antonio Soares (amsoares@netcabo.pt)
Date: Thu Jun 28 2007 - 08:09:39 ART

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Nothing better than an example from a live equipment:

++++++++++++++++++++++++++++++++++++++++++++++++++
With 802.1Q, we receive both PVST and PVST+ BPDU's
++++++++++++++++++++++++++++++++++++++++++++++++++

!
interface FastEthernet1/0/21
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,100
switchport mode trunk
!
2d12h: STP: VLAN0100 rx BPDU: config protocol = ieee, packet from
FastEthernet1/0/21 , linktype SSTP , enctype 3, encsize 22
2d12h: STP: enc 01 00 0C CC CC CD 00 11 5C 3D E6 95 00 32 AA AA 03 00 00 0C
01 0B
2d12h: STP: Data
0000000001806400115C3DE68000000000806400115C3DE68080150000140002000F00
2d12h: STP: VLAN0100 Fa1/0/21:0000 00 00 01 806400115C3DE680 00000000
806400115C3DE680 8015 0000 1400 0200 0F00
2d12h: STP(100) port Fa1/0/21 supersedes 0

2d12h: STP: VLAN0001 rx BPDU: config protocol = ieee, packet from
FastEthernet1/0/21 , linktype IEEE_SPANNING , enctype 2, encsize 17
2d12h: STP: enc 01 80 C2 00 00 00 00 11 5C 3D E6 95 00 26 42 42 03
2d12h: STP: Data
0000000000800100115C3DE68000000000800100115C3DE68080150000140002000F00
2d12h: STP: VLAN0001 Fa1/0/21:0000 00 00 00 800100115C3DE680 00000000
800100115C3DE680 8015 0000 1400 0200 0F00
2d12h: STP(1) port Fa1/0/21 supersedes 0

++++++++++++++++++++++++++++++++++++++++++++++++++
With ISL, we only receive PVST BPDU's
++++++++++++++++++++++++++++++++++++++++++++++++++

!
interface FastEthernet1/0/21
switchport trunk encapsulation isl
switchport trunk allowed vlan 1,100
switchport mode trunk
!
2d12h: STP: VLAN0100 rx BPDU: config protocol = ieee, packet from
FastEthernet1/0/21 , linktype IEEE_SPANNING , enctype 2, encsize 17
2d12h: STP: enc 01 80 C2 00 00 00 00 11 5C 3D E6 95 00 26 42 42 03
2d12h: STP: Data
0000000001806400115C3DE68000000000806400115C3DE68080150000140002000F00
2d12h: STP: VLAN0100 Fa1/0/21:0000 00 00 01 806400115C3DE680 00000000
806400115C3DE680 8015 0000 1400 0200 0F00
2d12h: STP(100) port Fa1/0/21 supersedes 0

2d12h: STP: VLAN0001 rx BPDU: config protocol = ieee, packet from
FastEthernet1/0/21 , linktype IEEE_SPANNING , enctype 2, encsize 17
2d12h: STP: enc 01 80 C2 00 00 00 00 11 5C 3D E6 95 00 26 42 42 03
2d12h: STP: Data
0000000001800100115C3DE68000000000800100115C3DE68080150000140002000F00
2d12h: STP: VLAN0001 Fa1/0/21:0000 00 00 01 800100115C3DE680 00000000
800100115C3DE680 8015 0000 1400 0200 0F00
2d12h: STP(1) port Fa1/0/21 supersedes 0

+++++++++++++++++++++++++++++++++++++++++++++

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Petr
Lapukhov
Sent: quinta-feira, 28 de Junho de 2007 9:12
To: thomas.rader@freesurf.ch
Cc: ccielab@groupstudy.com
Subject: Re: PVST vs PVST+

Simply put, PVST+ is a PVST implementation over 802.1q trunks, that
interoperates with 802.1q CST spanning-tree implementations.

PVST+ intends to "tunnel" PVST per-VLAN BPDUs through a "cloud" of
802.1qbridges
using special multicast MAC address, and at the same time, keeping in touch
with 802.1q CST.

So there is no actual difference in configuring these, they only differer
in operations.
PVST encapsulation/logic is used over ISL trunks, and PVST+ encapsulation
(differers a little from standard 802.1d) and logic is used over
802.1trunks. You can check out how PVST+ works on 802.1q trunk here:

http://puck.nether.net/pipermail/cisco-nsp/2004-March/009079.html

HTH

--
Petr Lapukhov, CCIE #16379 (R&S/Security/SP) petr@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
2007/6/28, thomas.rader@freesurf.ch <thomas.rader@freesurf.ch>:
>
> Hello,
>
> I'm confused about PVST vs PVST+
>
> Cisco talks about these as if they were seperate implementations 
> (PVST+ provides the same functionality as PVST using 802.1q instead of
ISL).
>
> However I can only find one method of PVST configuration in the CLI 
> and most of the documentation.
>
> Am I to assume that when Cisco talks about PVST they are actually 
> talking about PVST+ ?
>
>
> Per VLAN Spanning Tree (PVST)
>
> http://www.cisco.com/en/US/tech/tk389/tk621/tk846/tsd_technology_suppo
> rt_sub-protocol_home.html
>
> Per VLAN Spanning Tree Plus (PVST+)
>
> http://www.cisco.com/en/US/tech/tk389/tk621/tk847/tsd_technology_suppo
> rt_sub-protocol_home.html
>
>
> Thanks, Thomas
>
> ______________________________________________________________________
> _ Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

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