some strange cost factor coming in mstp

Created: Jul 1, 2019 17:41:35Latest reply: Jul 29, 2019 10:15:33 135 5 0 0
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Hi, I'm getting strange value in mstp cost in 5720-li -12tp connected to 5701-LI-28x. Below is the command for stp root br at 5720 switch


0.a0f4-79ab-3f71     201999     2  20      15 GigabitEthernet0/0/8

it should be 202000. It coming 1 less. Cant understandy why.

Thanks in adv for help

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Admin Created Jul 1, 2019 19:49:14 Helpful(0) Helpful(0)

Posted by hashbang at 2019-07-01 18:11 ty,its not isp network. Its our own network one connected with ofc and other with wireless (transpar ...
@hashbang Hi,
it would be helpful if you can upload the simple topology and the mstp configuration.
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All Answers
wissal MVE Created Jul 1, 2019 18:06:48 Helpful(0) Helpful(0)

Hello,

The key question here is whether your ISPs provide a transparent Layer2 interconnection between your switches 1 and 2, i.e. whether the ISP cloud behaves like a "cross-over cable" connecting the switches 1 and 2 together, and whether you can pass MSTP BPDUs through this Layer2 interconnect. If your ISPs do this then configuring what you require is simply a matter of modifying the MSTP costs just like you did. However, if the ISPs do not provide such transparent interconnection between switches 1 and 2 then it is simply not possible to accomplish this using MSTP because there is no Layer2 loop, and hence MSTP has nothing to act on - it must leave all ports unblocked for all instances in a loop-free environment.

Can you confirm that the interconnection between switches 1 and 2 as provided by the ISP cloud is a Layer2-transparent VPN capable of passing all your VLANs and MSTP communication?

Best regards,
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Telecommunications%20Engineer%2C%20currently%20senior%20project%20manager%20of%20the%20radio%20access%20network%20and%20partner%20of%20Huawei%20de%20Tunisia.
hashbang Created Jul 1, 2019 18:11:33 Helpful(0) Helpful(0)

ty,
its not isp network. Its our own network one connected with ofc and other with wireless (transparent bridge). There is already a stp loop-protection enabled and there is no port in abnormal state.
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chenhui Admin Created Jul 1, 2019 19:49:14 Helpful(0) Helpful(0)

Posted by hashbang at 2019-07-01 18:11 ty,its not isp network. Its our own network one connected with ofc and other with wireless (transpar ...
@hashbang Hi,
it would be helpful if you can upload the simple topology and the mstp configuration.
  • x
  • convention:

hashbang Created Jul 18, 2019 14:10:48 Helpful(0) Helpful(0)

Sorry for delays I was out of town
stp region-configuration
region-name R1
instance 1 vlan 101 to 199
instance 2 vlan 200 to 299
instance 3 vlan 500 to 599
instance 4 vlan 600 to 699
instance 5 vlan 700 to 799
instance 6 vlan 1500 to 1550            
instance 7 vlan 99 to 100 2000 4001
active region-configuration

interface GigabitEthernet0/0/8
description Cu
port link-type trunk
port trunk allow-pass vlan 100 614 617 620 to 621 2000
stp loop-protection
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chenhui Admin Created Jul 29, 2019 10:15:33 Helpful(0) Helpful(0)

Posted by hashbang at 2019-07-18 14:10 Sorry for delays I was out of townstp region-configuration region-name R1 instance 1 vlan 101 to 199 ...
the configuration indicates the instances of the MSTP and the VLANs binding with the instances. But the 20199 is the cost for instance 0, you'd better check the path from the S5720 to the STP root switch.
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