INE R&S ATC021 - MST with Multiple Regions

Inter-RegionMST

• MSTRegion is defined by
– VLANto instance mappings
– Region name
– Revision number
• Inter-Region path selection uses a CST
– Intra-region MSTIs are collapsed into CIST



MST Interoperability

• MST is backwards compatible with legacy CST (802.1d) and PVST+
• Behaves like Inter-Region MST
• CST Root must be within MST domain

 

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共有三個MST Instance 1 , MST Instance 2, MST Instance 3
每個MST都會有各自的Regional Root Switch............
就好像把SW1 & SW3 & others sw看成一台SW1,
SW2& others sw看成一台SW2, SW4& others sw看成一台SW4,

SW1 & SW2 & SW4中間會有一個MST Instance 0使用CST.....也會再推舉一個Root SW出來
這個CST Root SW必須一定要存在於MST1 or MST2 or MST3喔....

CST Root must be within MST domain
解釋: 若我們將SW4的MST3模式改成Rapid-PVST......這可以跟MST做Interoperability
          只要SW4不是CST Root即可........
          但若SW4剛好就是CST Root呢?
          這就無法跟MST做Interoperability...會有root inconsistent error的訊息...& BLK Port