Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
RSTP and MSTP
Marvin Rambhadjan
UvA
February 25, 2010
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Overview
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Rapid Spanning Tree Protocol
IEEE 802.1w 1998
Underlying protocol MSTP
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Similarities with STP
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Calculate the same spanning tree topology with the same
configuration
Differences with STP
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Faster conversion times
Different port states and new port roles
Different definition topology change
BPDUs used for Hello mechamism
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
RSTP Port States and Roles
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Port States
Forwarding
Learning
Disabled
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MAC Learning
Forwarding traffic
MAC Learning
No forwarding traffic
No MAC learning
No forwarding traffic
Port Roles
Root Port
Designated Port
Alternate Port
Backup Port
Disabled Port
Port to higher segments (to the Root Bridge)
Port to lower segments
Backup Root Port
Backup Designated Port
Not participating in RSTP
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Port Roles
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Definition Topology Change
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STP
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A Forwarding or Listening state port that transits to Blocking (lost
connection)
A port that transits in Forwarding state, while the switch already has
a Designated port (new connection)
RSTP
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Non-Edge port that transits in Forwarding (new connection)
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Rapid transit to Forwarding
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Edge Ports
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End stations
Not part of spanning tree process
Point to Point
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Connection between switches
Proposal and Agreement mechanism
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal and Agreement Mechanism
If a designated port wants to transits into a non-discarding state, the
upstream switch will do the following in order to agree with the
downstream switch.
1. Upstream Bridge sends proposal on Designated Port
2. Downstream Bridge receives proposal
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If it agrees on port role, it starts synchronization.
If it not agree on the proposal, it will send is own proposal
3. Downstream Bridge blocks all non-edge Designated Ports and send
Agreement to upstream bridge
4. Synchronization is needed to make sure there are no loops in the
topology when when the upstream bridge unblocks its Designated
Port
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal and Agreement
www.cisco.com
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal and Agreement
www.cisco.com
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal Agreement
www.cisco.com
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal Agreement
www.cisco.com
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Proposal Agreement
www.cisco.com
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Topology Changes
TC Detection
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Start TC While timer (2x Hello-Time) on all Non-Edge designated
and root ports
Flush all MAC addresses on these ports
Sends BPDUs with TC bit set, while TC While timer has not expired
TC Propagation
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Flush all MAC addresses on all ports except receiving port
Start TC While timer and sends BPDUs with TC bit set on all
Designated and Root ports
TCN not longer used
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Per VLAN Spanning Tree
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Many different variants
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Proprietary
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For both STP and RSTP
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Load Balancing
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Create independent spanning tree instances
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Single Spanning Tree
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Not all connections are used
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Per VLAN Spanning Tree
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10 Root Bridges
10 BPDU’s
10 Spanning Tree calculations
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Multiple Spanning Tree Protocol
IEEE 802.1s 2003
Built on RSTP
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MSTP vs (R)STP
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Use all links
MSTP vs PVST
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Minimize overhead
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Introduction Regions
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Two-Level Hierarchy
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Multiple independent Spanning Tree Instances
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
MSTP Terminology
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CIST Common Internal Spanning Tree
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CST Common Spanning Tree
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Topology of all “pseudo bridges”
IST (MSTI0) Internal Spanning Tree
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Topology of all switches in all regions
Spanning Tree within a region
Can communicate with other regions
Root Bridge election first based on External Path Cost
MSTIn Multiple Spanning Tree Instance n
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Spanning Tree within a region
Cannot communicate with other regions
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
MSTP parameters
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MSTP Region parameters
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VLAN-to-instance mapping
Configuration Name
Configuration Revision
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Root Priority per MSTI
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Path cost per MSTI
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Port Priority per MSTI
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example IST
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTIs
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
MSTP Multi Region
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Every region becomes a “pseudo-bridge”
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Topology of “pseudo-bridges” is called CST
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CST has no idea of internal MSTP regions
Hierarchy
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First Layer
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Common Internal Spanning Tree (CIST)
Collection of Internal Spanning Tree (IST)
Second Layer
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Internal Spanning Tree (IST)
Multiple Spanning Tree Instance(s) (MSTI)
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Multi Region Topology
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Multi Region Root Ports
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Multi Region Designated Ports
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Multi Region CIST
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP “Pseudo-Bridges CST
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Within a Region
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Example MSTP Within a Region
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Bridge Protocol Data Unit
Octet
1-2
3
4
5
6 - 13
14 - 17
18 - 25
26
28
30
32
34
36
37
-
27
29
31
33
35
- 38
39 - 102
BPDU
Protocol Identifier
Protocol Version Identifier
BPDU Type
CIST Flags
CIST Root Identifier
CIST External Path Cost
CIST Regional Root Identifier
CIST Port Identifier
Message Age
Max Age
Hello Time
Forward Delay
Version 1 Length
Version 3 Length
Content
Spanning Tree Protocol 0x0000
Multiple Spanning Tree 3
Rapid/Multiple Spanning Tree (0x02)
0
Number of octets in MSTP extension
64 octets MSTP Extension & 16 octets
per MSTI
MSTP Extension
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Bridge Protocol Data Unit
Octet
39
40 -71
72 - 73
74 - 89
90 - 93
94 - 101
102
Octet
1
2-9
10 - 13
14
15
16
MSTP Extension
MST Config ID Format Selector
MST Config Name
MST Revision
MST Config Digest
CIST Internal Path Cost
CIST Bridge Identifier
CIST Remaining Hops
MSTIDn
MSTID instance number
MSTI Flags
MSTI Regional Root Identifier
MSTI Internal Root Path Cost
MSTI Bridge Priority
MSTI Port Priority
MSTI Remaining Hops
Marvin Rambhadjan
Content
0
MSTI Instances
Content
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Flags
Bits
1
1
1
1
2
1
1
Description
Topology Change Acknowledgement
Agreement
Forwarding
Learning
Port Role
Proposal
Topology Change
Marvin Rambhadjan
RSTP and MSTP
Rapid Spanning Tree Protocol
Per VLAN Spanning Tree
Multiple Spanning Tree Protocol
Questions?
Marvin Rambhadjan
RSTP and MSTP