some strange cost factor coming in mstp

Created: Jul 1, 2019 17:41:35Latest reply: Jul 1, 2019 19:49:14 73 3 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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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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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:

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