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Name:HunterJoin In:Feb 21, 2019
iscussion / Help] [CCNP] MSTP is compatible with PVST+

Post by Hunter » Jan 28, 2019

1 Case configuration topology
2 Case configuration requirements
1. Configure the link between SW1 and SW2 as a trunk link, and the encapsulation protocol is dot1q.
2. Create VLAN 10, VLAN 11, VLAN 12 on SW1 and SW2 respectively.
3. SW1 runs the spanning tree protocol MSTP, and SW2 runs the spanning tree protocol PVST+ to achieve compatibility with different spanning trees.
3 Case Configuration Ideas
1. Configure the link between SW1 and SW2 as a trunk and encapsulate dot1q:
Interface FastEthernet0/21
Switchport trunk encapsulation dot1q / encapsulation protocol for dot1q/
Switchport modetrunk
2. Configure VLAN 10, VLAN 11, VLAN 12 on SW1 and SW2 respectively.
VLAN 10
Name VLAN0010
VLAN 11
Name VLAN0011
VLAN 12
Name VLAN0012
3. Set the SW1 spanning tree protocol to MSTP and set the IST (instance 0) priority to 0:
Spanning-tree mst configuration
Name region1
Spanning-treemode mst / Set the spanning tree protocol to mst/
Spanning-tree mst 0 priority 24576 / Modify IST (instance 0) has a priority of 24576, SW1 must be set to follow the bridge, otherwise it will not be compatible with PVST+ /
4. Configure the SW2 spanning tree protocol as PVST+:
Spanning-tree mode pvst / The default spanning tree protocol for Cisco switches is PVST+/
4 Case test results
1. View the spanning tree of SW1 instance 0:
SW1#showspan mst 0
##### MST0 vlansmapped: 1-4094
Bridge address 0018.b9da.5300 priority 24576 (24576 sysid0)
Root thisswitch for the CIST
Operational hellotime 2 , forward delay 15, max age 20, txholdcount 6
Configured hellotime 2 , forward delay 15, max age 20, max hops 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- ------------------ ----------------------
Fa0/21 DesgFWD 100 128.23 P2p Bound(PVST)
/Bound is the boundary port, which is the boundary between MSTP and PVST, and (PVST) is MSTP compatible with PVST/
2. Check the spanning tree running status of SW2 VLAN 10.
SW2#showspan vlan 10
VLAN0010
Spanning treeenabled protocol ieee
Root ID Priority 24576
Address 0018.b9da.5300
Cost 19
Port 21 (FastEthernet0/21)
HelloTime 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32778 (priority 32768 sys-id-ext10)
Address 000d.65ab.2800
HelloTime 2 sec Max Age 20 sec Forward Delay 15 sec
AgingTime 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- ---------- ----------------------
Fa0/21 Root FWD 19 128.21 P2p / This port is with port /
5 case configuration file
MSTP-PVST (MSTP SW is the bridge) - SW1 configuration.txt (13.94 KB, Downloads: 48)
MSTP-PVST (MSTP SW is the bridge) - SW2 configuration.txt (25.77 KB, Downloads: 34)
6 Case data capture
1. The BPDU packet received by SW2 starts the debug switch that receives the BPDU:
SW2#debug spanning-tree bpdu receive
SpanningTree BPDU Received debugging is on
SW2#
01:20:25:STP: VLAN0001 rx BPDU: config protocol = ieee, packet fromFastEthernet0/21, linktypeIEEE_SPANNING, enctype 2, encsize 17
01:20:25:STP: enc 01 80 C2 00 00 00 00 18 B9 DA 53 17 00 26 42 42 03
01:20:25:STP:Data 000000000060000018B9DA53000000000060000018B9DA530080170000140002000F00
01:20:25:STP: VLAN0001 Fa0/21:0000 00 00 00 60000018B9DA5300 00000000 60000018B9DA53008017 0000 1400 0200 0F00
01:20:25:STP(1) port Fa0/21 supersedes 0
01:20:25:STP: VLAN0010 rx BPDU: config protocol = ieee, packet from FastEthernet0/21, linktype SSTP, enctype 3, encsize 22
01:20:25:STP: enc 01 00 0C CC CC CD 00 18 B9 DA 53 17 00 32 AA AA 03 00 00 0C 01 0B
01:20:25:STP:Data 000000000060000018B9DA53000000000060000018B9DA530080170000140002000F00
01:20:25:STP: VLAN0010 Fa0/21:0000 00 00 00 60000018B9DA5300 00000000 60000018B9DA53008017 0000 1400 0200 0F00
01:20:25:STP(10) port Fa0/21 supersedes 96
01:20:25:STP: VLAN0011 rx BPDU: config protocol = ieee,packet from FastEthernet0/21
SW2#, linktype SSTP , enctype 3, encsize 22
01:20:25:STP: enc 01 00 0C CC CC CD 00 18 B9 DA 53 17 00 32 AA AA 03 00 00 0C 01 0B
01:20:25:STP:Data 000000000060000018B9DA53000000000060000018B9DA530080170000140002000F00
01:20:25:STP: VLAN0011 Fa0/21:0000 00 00 00 60000018B9DA5300 00000000 60000018B9DA53008017 0000 1400 0200 0F00
01:20:25:STP(11) port Fa0/21 supersedes 0
01:20:25:STP: VLAN0012 rx BPDU: config protocol = ieee, packet from FastEthernet0/21, linktype SSTP, enctype 3, encsize 22
SW2#
01:20:25:STP: enc 01 00 0C CC CC CD 00 18 B9 DA 53 17 00 32 AA AA 03 00 00 0C 01 0B
01:20:25:STP:Data 000000000060000018B9DA53000000000060000018B9DA530080170000140002000F00
01:20:25:STP: VLAN0012 Fa0/21:0000 00 00 00 60000018B9DA5300 00000000 60000018B9DA53008017 0000 1400 0200 0F00
01:20:25:STP(12) port Fa0/21 supersedes 0
/SSTP is the SharedSpanning Tree Protocol. This BPDU/ is sent using PVST+ MAC 0100.0ccc.cccd.
7 Case summary and other
1. When configuring MSTP and PVST+ spanning tree to be compatible, you must ensure that the MSTP switch is a follower bridge.
2. If one or more VLANs on the PVST+ switch are bridges, the port that connects the MSTP switch to the PVST+ switch is set to PVST inconsistency (*PVST_Inc), and the port status is set to (BKN*). Resulting in data not being forwarded;
E.g:
In this case, the priority of VLAN 10 of the PVST+ switch is 0:
SW2(config)#spanning-tree vlan 10priority 0
The SW1 switch first receives the following message, meaning that a better BPDU has been received:
SW1#
*Mar 1 01:17:00.805: %SPANTREE-2-PVSTSIM_FAIL:Blocking designated port Fa0/21: Inconsitent superiorPVST BPDU received on VLAN 10, claiming root 10:000d.65ab.2800
*Mar 1 01:17:01.812: %LINEPROTO-5-UPDOWN: Lineprotocol on Interface Vlan11, changed state to down
At this time, SW2 directly sets the port status to BKN*. In this environment, the Cisco software version can only implement the MSTP switch as a follower bridge. Otherwise, the phenomenon described at the beginning will occur. The specific phenomenon is as follows:
SW1#show span mst 0
##### MST0 vlans mapped: 1-4094
Bridge address 0018.b9
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