08-21-2012 03:59 PM - edited 03-07-2019 08:28 AM
Hi All,
I have read in ine MST tutorial that a switch does not exchange M-Records out the Boundary Port, i.e, a pot connected to either another MST Region or an STP/RSTP switch.
My question is that how does a switch knows that it's certain port is Boundary Port ? As far as i guess, initially a switch will emit MST BPDU with M-Records, but when it recieves MST BPDU from another Region with a different Region Name, it will mark it's port Boundary and will cease sending M-Records out this port.
Can someone please explain it a bit more ????
Regards,
Daud Parvez
Solved! Go to Solution.
08-21-2012 07:01 PM
Hello Daud,
You are very correct in your understanding. The switch will indeed start by sending MST BPDUs on all its Designated ports. However, if it receives a MST BPDU that has either a different region name, revision or the MD5 hash of the VLAN-to-instance mapping table, or that is not a MST BPDU at all, the switch will mark the receiving port as a boundary port, knowing that the neighboring switch is configured differently.
Now, if the neighboring switch runs MSTP but in a different region, the switches will continue to send MST BPDUs including the M-records. However, knowing that the neighbor is in a different MST region, both switches will process only the CIST parts of the MST BPDU, ignoring other M-records.
If the neighboring switch runs a different STP version, the MST switch will fall back to using that version on the appropriate port.
Please feel welcome to ask further!
Best regards,
Peter
08-21-2012 07:01 PM
Hello Daud,
You are very correct in your understanding. The switch will indeed start by sending MST BPDUs on all its Designated ports. However, if it receives a MST BPDU that has either a different region name, revision or the MD5 hash of the VLAN-to-instance mapping table, or that is not a MST BPDU at all, the switch will mark the receiving port as a boundary port, knowing that the neighboring switch is configured differently.
Now, if the neighboring switch runs MSTP but in a different region, the switches will continue to send MST BPDUs including the M-records. However, knowing that the neighbor is in a different MST region, both switches will process only the CIST parts of the MST BPDU, ignoring other M-records.
If the neighboring switch runs a different STP version, the MST switch will fall back to using that version on the appropriate port.
Please feel welcome to ask further!
Best regards,
Peter
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