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STP chenshh Why STP? Computer Center, CS, NCTU 2 Computer - - PowerPoint PPT Presentation
STP chenshh Why STP? Computer Center, CS, NCTU 2 Computer - - PowerPoint PPT Presentation
STP chenshh Why STP? Computer Center, CS, NCTU 2 Computer Center, CS, NCTU Problems 1.Broadcast Storms 2.Mac-Table Inestability 3.Multiples copies of frames 3 Computer Center, CS, NCTU Basic STP (802.1d) Before we start we need talks
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Problems
1.Broadcast Storms 2.Mac-Table Inestability 3.Multiples copies of frames
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Basic STP (802.1d)
Before we start we need talks about these 1.Bridge Protocol Data Unit(L2) 2.Bridge ID
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BPDU
1.L2 -> MAC Address 2.Sent to a specail multicast address 01:80:C2:00:00:00
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Bridge ID
Generate by switch macs and its prioriy The default priority is 32768
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How STP works?
1.Root Bridge Election 2.Set port state
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Root Bridge Election Passing BPDUs,Choosing the smallest bridge id as root bridge.
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Set port role
Three roles: Root port Designated port Block port
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Calculate Costs
We want the cost to root be minimal! Set the right root port1
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Setting states
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Setting states
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Some tips
Who is root is important!
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Some Issues
1.When changing states temporary cycles may appear. 2.Using timeouts is slow.
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Set port state
Five States: Blocking Listening Learning Forwarding Disabled Each transitions between state cost several seconds Will not generate loops!
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RSTP (802.1w)
Minify response time to several seconds Compatibility of STP
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More roles
Root Designated Alternative Backup Disabled Edge
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VLAN Issues
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Cisco’s PVST
One VLAN One STP 802.1q tagged modified BDPU
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Cisco’s PVST+
Run STP at VLAN 1 Run PVST at others Compatibility of STP/RSTP
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Cisco’s Rapid-PVST+
Add RSTP features
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Some Issues
One VLAN -> One STP Hundreds VLAN -> Hundreds STP Massive PVST BPDUs on the networks Massive Calculations And these are cisco’s protocol not well supported on other manufacturers’ products
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MSTP
MST Region MST Instance CIST
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MST Region
Looks like a switch from outside
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MST Instances
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