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IEEE 802.1S, CZYLI STP
JESZCZE NIE UMARŁO
Piotr Wojciechowski (CCIE #25543)
ABOUT ME
¢ Senior Network Engineer MSO at VeriFone Inc.
¢ Previously Network Solutions Architect at one of top polish IT
i...
ABOUT CCIE.PL
¢ The biggest Cisco community in Europe
¢ Over 8300 users
¢ Strong staff
— 3 general admins
— 1 board admin
...
AGENDA
¢ Why MST is not dead, where we can use them?
¢ Basic MST definition
¢ How MST works within single region
¢ How MST...
MULTIPLE SPANNING TREE PROTOCOL
IEEE 802.1S
802.1S - MST
¢ Key words about MST:
— IEEE standard, vendor independent
— Spanning-tree per defined group of VLANs
— Multi...
802.1S - MST
¢ When we should consider using 802.1s:
— Multivendor L2 network
— Increased cost of blocked (unused) physica...
802.1S - MST
¢ When you should not use MSTP:
— MSTP may not converge as fast as RSTP
— You are afraid of configuration com...
A LITTLE BIT OF THEORY OF MST
MSTP – BASIC DEFINITIONS
¢ MST segments network into one or multiple regions
— Region is group of switches that run MST in...
MSTP – BASIC DEFINITIONS
¢ MST bridge must be able to handle at least two instances:
— One Internal Spanning Tree (IST)
— ...
MSTP – BASIC DEFINITIONS
¢ Two special type of trees are build
— Internal Spanning Tree (IST) or Multiple Spanning Tree In...
MSTP – BASIC DEFINITIONS
¢ BPDU
— Single BPDU carries information about all instances
— Is only exchanged on MSTI0 instanc...
MSTP – BASIC DEFINITIONS
¢ BPDU M-records
— By default all VLANs are mapped to IST (no configuration needed)
¢ Provides cl...
MST SINGLE REGION
¢ Topology
spanning-tree mst configuration
name PLNOG-EU
revision 1
instance 1 vlan 11-13
instance 2 vla...
MST SINGLE REGION
¢ Configuration
Switch Warsaw
Warsaw#show spanning-tree
MST0
Spanning tree enabled protocol mstp
Root ID...
MST SINGLE REGION
MST2
Spanning tree enabled protocol mstp
Root ID Priority 2
Address fa16.3ee6.4bad
This bridge is the ro...
MST SINGLE REGION
¢ BPUD
From Warsaw to Berlin
Interface ge0/1
Frame 9: 151 bytes on wire (1208 bits), 151 bytes captured ...
MST SINGLE REGION
Frame 9: 151 bytes on wire (1208 bits), 151 bytes captured (1208 bits)
IEEE 802.3 Ethernet
Logical-Link ...
MST BPDU
QUIZ!
¢ Two questions – two prizes
— First question easier
— Second question a little bit harder
¢ What I can win?
— Corre...
QUIZ – QUESTION #1
¢ Maximum of how many instances (except MST0) are allowed by
standard IEEE 802.1s-2002?
64
Defined in p...
QUIZ – QUESTION #2
¢ In typical Ethernet network (no tuned parameters) theoretically
maximum of how many instances (except...
QUIZ – QUESTION #2
¢ In typical Ethernet network (no tuned parameters) theoretically
maximum of how many instances (except...
MSTP DESIGN CONSIDERATIONS
VLAN MAPPING
MSTP DESIGN CONSIDERATIONS
¢ MSTP is not PVST+ - spanning-tree instances are not mapped one-to-
one to VLANs
¢ Misconfigur...
MSTP DESIGN CONSIDERATIONS
SWITCH STACKS
MSTP AND SWITCH STACK
¢ A switch stack appears as a single spanning-tree node to the rest of the
network
¢ All stack membe...
MSTP AND SWITCH STACK
¢ If a switch that does not support MSTP is added to stack the switch is
put into a version mismatch...
MSTP DESIGN CONSIDERATIONS
MSTP AND NEWER TECHNOLOGIES
MSTP AND FABRICPATH
¢ Design requirements:
— All of the FP switches must be seen by the attached devices as a single switc...
MSTP – PLATFORM CAVEATS
¢ Look out for platform specific bugs that may affect your network
¢ Example: CSCuj23131 - Bridgin...
MSTP DESIGN CONSIDERATIONS
MULTI-REGION
MSTP MULTI-REGION
¢ Why we would like to have multiple regions not just multiple
instances?
— Introducing boundary of STP ...
MSTP MULTI-REGION
¢ Configuration
Switch: Toronto
spanning-tree mode mst
!
spanning-tree mst configuration
name PLNOG-US
r...
MSTP MULTI-REGION
¢ Spanning tree
Switch: Toronto
Toronto#show spanning-tree vlan 11
MST1
Spanning tree enabled protocol m...
MSTP MULTI-REGION
¢ Spanning tree
Switch: Vancouver
Vancouver#show spanning-tree vlan 11
MST1
Spanning tree enabled protoc...
MSTP MULTI-REGION
¢ Spanning tree
Switch: Montreal
Montreal#show spanning-tree vlan 11
MST1
Spanning tree enabled protocol...
MSTP DESIGN CONSIDERATIONS
MST AND PVST+
MST AND PVST+
¢ Every switch in PVST+ domain perceive MST zone as virtual switch
with multiple boundary ports
¢ Topology c...
MST AND PVST+
¢ CST Root Bridge in MST region
— If there is only one MST region connected to PVST+ then all boundary ports...
MST AND PVST+
¢ Topology
Note:
¢ Same VLANs defined on all switches
¢ PVST+ with default STP priorities
MST AND PVST+
¢ BPDU
Switch: Toronto
Frame 7: 68 bytes on wire (544 bits), 68 bytes captured (544 bits)
Ethernet II, Src: ...
MST AND PVST+
¢ Spanning-tree
Switch: Berlin
Berlin#show spanning-tree vlan 11
MST1
Spanning tree enabled protocol mstp
Ro...
MST AND PVST+
¢ Spanning-tree
Switch: Warsaw
Warsaw#show spanning-tree vlan 11
MST1
Spanning tree enabled protocol mstp
Ro...
MST AND PVST+
¢ Spanning-tree
Switch: Toronto
Toronto#show spanning-tree vlan 11
VLAN0011
Spanning tree enabled protocol i...
MST AND PVST+
¢ Spanning-tree
Switch: Montreal
Montreal#show spanning-tree vlan 11
VLAN0011
Spanning tree enabled protocol...
MST AND PVST+
MSTP RESTRICTIONS
¢ PVST+, Rapid PVST+, and MSTP are supported, but only one version
can be active at any time
¢ VLAN Trun...
MSTP RESTRICTIONS
¢ Spanning-tree protocols interoperability
PVST+ MSTP Rapid PVST+
PVST+ Yes Yes (with restrictions) Yes ...
MSTP DESIGN CONSIDERATIONS
MIGRATION TO 802.1S
MIGRATION TO 802.1S
¢ It’s not possible to convert all of the switches at the same time
¢ So let’s take an advantage of ba...
MIGRATION TO 802.1S
¢ Step #1
Make proper network documentation!
— If you don’t know your network you will break something...
MIGRATION TO 802.1S
¢ Step #2
Review vendor whitepapers and documentation
— There always may be some limitation
— There mi...
MIGRATION TO 802.1S
¢ Step #3
Review trunks configuration
— Trunks should carry all the VLANs that are mapped to an instan...
MIGRATION TO 802.1S
¢ Step #5
Know your roots
— Configure roots on switches that will be roots for particular instance
¢ E...
MIGRATION TO 802.1S
¢ Step #6
Start from root, then work your way down
— Remember that “new” root MST switch will temporar...
MIGRATION TO 802.1S
¢ Step #7
Monitoring
— Carefully check STP calculations
¢ Maybe some ports you wanted in Forwarding st...
QUESTIONS?
THANK YOU
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PLNOG 17 - Piotr Wojciechowski - 802.1s MST, czyli STP u operatora i w DC nie umarło a nawet ma się dobrze w środowiskach multi-vendor

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Protokół spanning-tree - wypierany przez inne technologie w nowoczesnych rozwiązaniach nadal stanowi podstawę działania sieci. Wśród wielu jego odmian trochę zapomniane i niedocenione wcielenie stanowi 802.1s czyli MST. Sesja ma na celu przypomnienie podstaw działania MST i wskazanie scenariuszy, w których protokół ten może ułatwić nam życie.

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PLNOG 17 - Piotr Wojciechowski - 802.1s MST, czyli STP u operatora i w DC nie umarło a nawet ma się dobrze w środowiskach multi-vendor

  1. 1. IEEE 802.1S, CZYLI STP JESZCZE NIE UMARŁO Piotr Wojciechowski (CCIE #25543)
  2. 2. ABOUT ME ¢ Senior Network Engineer MSO at VeriFone Inc. ¢ Previously Network Solutions Architect at one of top polish IT integrators ¢ CCIE #25543 (Routing & Switching) ¢ PLNOG Advisory Board member ¢ CCIE.PL General Admin It’s 10th edition of PLNOG where I’m a speaker!
  3. 3. ABOUT CCIE.PL ¢ The biggest Cisco community in Europe ¢ Over 8300 users ¢ Strong staff — 3 general admins — 1 board admin — 3 servers admins — 3 moderators ¢ Over 60 polish CCIEs as members — over 20 of them actively posting! ¢ About 100 new topics per month ¢ About 800 posts per month ¢ English section available
  4. 4. AGENDA ¢ Why MST is not dead, where we can use them? ¢ Basic MST definition ¢ How MST works within single region ¢ How MST works in multiple regions configuration ¢ How MST works with non-MST switches ¢ Migration to MST and other caveats we have to remember when designing MST network
  5. 5. MULTIPLE SPANNING TREE PROTOCOL IEEE 802.1S
  6. 6. 802.1S - MST ¢ Key words about MST: — IEEE standard, vendor independent — Spanning-tree per defined group of VLANs — Multiple instances per region — Multiple regions — Can work together with RSTP, PVSTP+ etc.
  7. 7. 802.1S - MST ¢ When we should consider using 802.1s: — Multivendor L2 network — Increased cost of blocked (unused) physical links — Large L2 domains, PVST+ protocol with big amount of VLANs and frequent changes are causing lots of recalculations ¢ CPU saturation ¢ Memory saturation — Limit of number of STP instances on some platforms (in example Cisco Catalyst 2960 or 3560) for per-VLAN protocols (PVST+ and RPVST+) — If you are not ready to replace STP with routing
  8. 8. 802.1S - MST ¢ When you should not use MSTP: — MSTP may not converge as fast as RSTP — You are afraid of configuration complexity ¢ All switches must be reconfigured when VLAN mapping changes
  9. 9. A LITTLE BIT OF THEORY OF MST
  10. 10. MSTP – BASIC DEFINITIONS ¢ MST segments network into one or multiple regions — Region is group of switches that run MST in consistent way: ¢ Same number of instances ¢ Same set of VLANs in each instance ¢ Same configuration name ¢ Same revision number — Each switch in the region has a single MST configuration ¢ Maximum of 65 active instances per region (instance 0 and 64 user-defined instances) ¢ Single BPDU carry information about all instances
  11. 11. MSTP – BASIC DEFINITIONS ¢ MST bridge must be able to handle at least two instances: — One Internal Spanning Tree (IST) — One or more Multiple Spanning Tree Instances — Sub-optimal paths between regions and non-MST switches may happen
  12. 12. MSTP – BASIC DEFINITIONS ¢ Two special type of trees are build — Internal Spanning Tree (IST) or Multiple Spanning Tree Instance 0 (MSTI0) ¢ Only this instance that interact with switches “external” to the region ¢ Has root bridge (CIST Regional Roots) ¢ Carries BPDU with information for all instances — Common Spanning Tree (CST) ¢ Build spanning-tree across regions ¢ Interoperates with the STP/RSTP regions ¢ Elects CST Root based on CIST Regional Roots
  13. 13. MSTP – BASIC DEFINITIONS ¢ BPDU — Single BPDU carries information about all instances — Is only exchanged on MSTI0 instance — Contain all standard RSTP-style information for the IST itself — Carry additional informational fields ¢ Configuration name ¢ Revision numer ¢ Hash value calculated over VLANs to MSTI mapping table contents Switch may detect mis-configuration in VLAN mappings by comparing the hash value received from the peer with the local value
  14. 14. MSTP – BASIC DEFINITIONS ¢ BPDU M-records — By default all VLANs are mapped to IST (no configuration needed) ¢ Provides classic RSTP implementation where all VLANs share same STP — Information about other instances is glued to BPDU as M-records using TLV (Type-Length-Value) type of fields ¢ One M-record per instance ¢ Each M-record contain ¢ Root priority ¢ Designated bridge priority ¢ Port Priority ¢ Root path cost ¢ Other information
  15. 15. MST SINGLE REGION ¢ Topology spanning-tree mst configuration name PLNOG-EU revision 1 instance 1 vlan 11-13 instance 2 vlan 21-22 spanning-tree mst 0 priority 61440 spanning-tree mst 1 priority 61440 spanning-tree mst 2 priority 61440 spanning-tree mst configuration name PLNOG-EU revision 1 instance 1 vlan 11-13 instance 2 vlan 21-22 spanning-tree mst 0 priority 4096 spanning-tree mst 1 priority 0 spanning-tree mst 2 priority 4096 spanning-tree mst configuration name PLNOG-EU revision 1 instance 1 vlan 11-13 instance 2 vlan 21-22 spanning-tree mst 0 priority 0 spanning-tree mst 1 priority 4096 spanning-tree mst 2 priority 0 spanning-tree mode mst spanning-tree mode mst spanning-tree mode mst
  16. 16. MST SINGLE REGION ¢ Configuration Switch Warsaw Warsaw#show spanning-tree MST0 Spanning tree enabled protocol mstp Root ID Priority 0 Address fa16.3ee6.4bad This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 0 (priority 0 sys-id-ext 0) Address fa16.3ee6.4bad Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Gi0/1 Desg FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3ed7.dcbf Cost 20000 Port 2 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 4097 (priority 4096 sys-id-ext 1) Address fa16.3ee6.4bad Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Gi0/1 Root FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr
  17. 17. MST SINGLE REGION MST2 Spanning tree enabled protocol mstp Root ID Priority 2 Address fa16.3ee6.4bad This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 2 (priority 0 sys-id-ext 2) Address fa16.3ee6.4bad Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- Gi0/1 Desg FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr ¢ Configuration Switch Warsaw
  18. 18. MST SINGLE REGION ¢ BPUD From Warsaw to Berlin Interface ge0/1 Frame 9: 151 bytes on wire (1208 bits), 151 bytes captured (1208 bits) IEEE 802.3 Ethernet Logical-Link Control Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Multiple Spanning Tree (3) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x7c, Agreement, Forwarding, Learning, Port Role: Designated Root Identifier: 0 / 0 / fa:16:3e:e6:4b:ad Root Path Cost: 0 Bridge Identifier: 0 / 0 / fa:16:3e:e6:4b:ad Port identifier: 0x8002 Message Age: 0 Max Age: 20 Hello Time: 2 Forward Delay: 15 Version 1 Length: 0 Version 3 Length: 96 MST Extension MST Config ID format selector: 0 MST Config name: PLNOG-EU MST Config revision: 1 MST Config digest: 76109677309c059d469ecb122efbc871 CIST Internal Root Path Cost: 0 CIST Bridge Identifier: 0 / 0 / fa:16:3e:e6:4b:ad CIST Bridge Priority: 0 CIST Bridge Identifier System ID Extension: 0 CIST Bridge Identifier System ID: fa:16:3e:e6:4b:ad (fa:16:3e:e6:4b:ad) CIST Remaining hops: 20 MSTID 1, Regional Root Identifier 0 / fa:16:3e:d7:dc:bf MSTI flags: 0x38, Forwarding, Learning, Port Role: Root 0000 .... = Priority: 0x0 .... 0000 0000 0001 = MSTID: 1 Regional Root: fa:16:3e:d7:dc:bf (fa:16:3e:d7:dc:bf) Internal root path cost: 20000 Bridge Identifier Priority: 1 Port identifier priority: 8 Remaining hops: 20 MSTID 2, Regional Root Identifier 0 / fa:16:3e:e6:4b:ad MSTI flags: 0x7c, Agreement, Forwarding, Learning, Port Role: Designated 0000 .... = Priority: 0x0 .... 0000 0000 0010 = MSTID: 2 Regional Root: fa:16:3e:e6:4b:ad (fa:16:3e:e6:4b:ad) Internal root path cost: 0 Bridge Identifier Priority: 0 Port identifier priority: 8 Remaining hops: 20
  19. 19. MST SINGLE REGION Frame 9: 151 bytes on wire (1208 bits), 151 bytes captured (1208 bits) IEEE 802.3 Ethernet Logical-Link Control Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Multiple Spanning Tree (3) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x7c, Agreement, Forwarding, Learning, Port Role: Designated Root Identifier: 0 / 0 / fa:16:3e:e6:4b:ad Root Path Cost: 0 Bridge Identifier: 0 / 0 / fa:16:3e:e6:4b:ad Port identifier: 0x8002 Message Age: 0 Max Age: 20 Hello Time: 2 Forward Delay: 15 Version 1 Length: 0 Version 3 Length: 96 MST Extension MST Config ID format selector: 0 MST Config name: PLNOG-EU MST Config revision: 1 MST Config digest: 76109677309c059d469ecb122efbc871 CIST Internal Root Path Cost: 0 CIST Bridge Identifier: 0 / 0 / fa:16:3e:e6:4b:ad CIST Bridge Priority: 0 CIST Bridge Identifier System ID Extension: 0 CIST Bridge Identifier System ID: fa:16:3e:e6:4b:ad (fa:16:3e:e6:4b:ad) CIST Remaining hops: 20 MSTID 1, Regional Root Identifier 0 / fa:16:3e:d7:dc:bf MSTI flags: 0x38, Forwarding, Learning, Port Role: Root 0000 .... = Priority: 0x0 .... 0000 0000 0001 = MSTID: 1 Regional Root: fa:16:3e:d7:dc:bf (fa:16:3e:d7:dc:bf) Internal root path cost: 20000 Bridge Identifier Priority: 1 Port identifier priority: 8 Remaining hops: 20 MSTID 2, Regional Root Identifier 0 / fa:16:3e:e6:4b:ad MSTI flags: 0x7c, Agreement, Forwarding, Learning, Port Role: Designated 0000 .... = Priority: 0x0 .... 0000 0000 0010 = MSTID: 2 Regional Root: fa:16:3e:e6:4b:ad (fa:16:3e:e6:4b:ad) Internal root path cost: 0 Bridge Identifier Priority: 0 Port identifier priority: 8 Remaining hops: 20 Image source: http://blog.ine.com/2010/02/22/understanding-mstp/
  20. 20. MST BPDU
  21. 21. QUIZ! ¢ Two questions – two prizes — First question easier — Second question a little bit harder ¢ What I can win? — Correct answer for first question takes a book — Correct answer for second question takes voucher for half-year subscription of IT Professional magazine
  22. 22. QUIZ – QUESTION #1 ¢ Maximum of how many instances (except MST0) are allowed by standard IEEE 802.1s-2002? 64 Defined in paragraph 13.14: “No more than 64 MSTI Configuration Messages may be encoded in an MST BPDU,and no more than 64 MSTIs may be supported by an MST Bridge”
  23. 23. QUIZ – QUESTION #2 ¢ In typical Ethernet network (no tuned parameters) theoretically maximum of how many instances (except MST0) might be supported and why? 87
  24. 24. QUIZ – QUESTION #2 ¢ In typical Ethernet network (no tuned parameters) theoretically maximum of how many instances (except MST0) might be supported and why? 87 Typical MTU on Ethernet network is 1500B 1500B – (size of BPDU header and CIST) 1500B – 102B = 1398B 1398B / (size of M-record) 1398B / 16B = 87.375
  25. 25. MSTP DESIGN CONSIDERATIONS VLAN MAPPING
  26. 26. MSTP DESIGN CONSIDERATIONS ¢ MSTP is not PVST+ - spanning-tree instances are not mapped one-to- one to VLANs ¢ Misconfiguration or VLAN pruning may result in situation where filtering is not consistent with the respective MSTI blocking decisions — Solution? Don’t use static VLAN pruning VLANs 10,20 mapped to MSTI2 Trunk allowing VLAN 10 Trunk allowing VLAN 20 MSTI2 is blocking port where VLAN20 is permitted X
  27. 27. MSTP DESIGN CONSIDERATIONS SWITCH STACKS
  28. 28. MSTP AND SWITCH STACK ¢ A switch stack appears as a single spanning-tree node to the rest of the network ¢ All stack members use the same bridge ID for a given spanning tree — The bridge ID is derived from the MAC address of the active switch ¢ If the switch stack is the spanning-tree root and the active switch fails or leaves the stack: — The standby switch becomes the new active switch — Bridge IDs remain the same — Spanning-tree reconvergence might occur
  29. 29. MSTP AND SWITCH STACK ¢ If a switch that does not support MSTP is added to stack the switch is put into a version mismatch state — Automatically upgraded or downgraded to the same version of software that is running on the switch stack ¢ Using any form of stacking, clustering or other virtualization methods always refer to documentation – behavior may differ depending on vendor, platform, technology and firmware version
  30. 30. MSTP DESIGN CONSIDERATIONS MSTP AND NEWER TECHNOLOGIES
  31. 31. MSTP AND FABRICPATH ¢ Design requirements: — All of the FP switches must be seen by the attached devices as a single switch that acts as the root of the STP domain: ¢ They must share a common bridge ID (c84c.75fa.6000 + STP domain number) inside each STP domain ¢ The domain number can be changed with the spanning-tree domain [id] command ¢ Set the priority of the FP switches so that they become the root of the STP domain ¢ Use spanning-tree vlan [vlan] priority 0 ¢ Ensure that the attached STP switches have an STP priority that is set higher than the FP switches
  32. 32. MSTP – PLATFORM CAVEATS ¢ Look out for platform specific bugs that may affect your network ¢ Example: CSCuj23131 - Bridging Loop with MST and FabricPath — Symptom: Under the following conditions, STP topology can converge without blocking where necessary leading to a bridging loop: 1. Spanning-tree mode MST containing multiple MST regions. 2. FabricPath leaf switches are in one MST region. 3. CE Switches are in a different MST region (than the FabricPath switches) 4. No FabricPath VLANs mapped to MST instance 0 — Workaround: This scenario can be avoided by one of the following: 1. Configure MST such that there is only one MST region. OR 2. Map at least one FabricPath VLAN to MST instance 0. — Known Affected Releases: 6.2(2)
  33. 33. MSTP DESIGN CONSIDERATIONS MULTI-REGION
  34. 34. MSTP MULTI-REGION ¢ Why we would like to have multiple regions not just multiple instances? — Introducing boundary of STP calculations — Logical administrative separation – useful during migrations or when networks of two companies merge
  35. 35. MSTP MULTI-REGION ¢ Configuration Switch: Toronto spanning-tree mode mst ! spanning-tree mst configuration name PLNOG-US revision 1 instance 1 vlan 11-13 instance 2 vlan 21-22 ! spanning-tree mst 0-2 priority 0
  36. 36. MSTP MULTI-REGION ¢ Spanning tree Switch: Toronto Toronto#show spanning-tree vlan 11 MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3e47.3e34 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 1 (priority 0 sys-id-ext 1) Address fa16.3e47.3e34 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Desg FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr Gi0/3 Desg FWD 20000 128.4 Shr
  37. 37. MSTP MULTI-REGION ¢ Spanning tree Switch: Vancouver Vancouver#show spanning-tree vlan 11 MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3e47.3e34 Cost 20000 Port 3 (GigabitEthernet0/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address fa16.3e7f.8215 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Altn BLK 20000 128.2 Shr Gi0/2 Root FWD 20000 128.3 Shr Gi0/3 Desg FWD 20000 128.4 Shr
  38. 38. MSTP MULTI-REGION ¢ Spanning tree Switch: Montreal Montreal#show spanning-tree vlan 11 MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3e47.3e34 Cost 20000 Port 3 (GigabitEthernet0/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address fa16.3e7b.e611 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Desg FWD 20000 128.2 Shr Gi0/2 Root FWD 20000 128.3 Shr
  39. 39. MSTP DESIGN CONSIDERATIONS MST AND PVST+
  40. 40. MST AND PVST+ ¢ Every switch in PVST+ domain perceive MST zone as virtual switch with multiple boundary ports ¢ Topology change of PVST+ tree will impact every MSTI instance in all MSTP regions because CST tree must be recalculated ¢ Switches both in MST and non-MST domain have to build CST and elect CST Root Bridge
  41. 41. MST AND PVST+ ¢ CST Root Bridge in MST region — If there is only one MST region connected to PVST+ then all boundary ports will be unblocked and can be used by PVST+ trees ¢ CST Root Bridge in PVST+ domain — Not recommended design — No load-balancing between multiple links ¢ Cisco support only CST Root Bridge in MST region! — If CST Root Bridge is not in MST domain boundary ports will be put in root- inconsistent state
  42. 42. MST AND PVST+ ¢ Topology Note: ¢ Same VLANs defined on all switches ¢ PVST+ with default STP priorities
  43. 43. MST AND PVST+ ¢ BPDU Switch: Toronto Frame 7: 68 bytes on wire (544 bits), 68 bytes captured (544 bits) Ethernet II, Src: fa:16:3e:aa:56:50 (fa:16:3e:aa:56:50), Dst: PVST+ (01:00:0c:cc:cc:cd) 802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 21 Logical-Link Control Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Spanning Tree (0) BPDU Type: Configuration (0x00) BPDU flags: 0x00 Root Identifier: 0 / 0 / fa:16:3e:e6:4b:ad Root Path Cost: 0 Bridge Identifier: 4096 / 0 / fa:16:3e:d7:dc:bf Port identifier: 0x8004 Message Age: 0 Max Age: 20 Hello Time: 2 Forward Delay: 15 Originating VLAN (PVID): 21 Type: Originating VLAN (0x0000) Length: 2 Originating VLAN: 21
  44. 44. MST AND PVST+ ¢ Spanning-tree Switch: Berlin Berlin#show spanning-tree vlan 11 MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3ed7.dcbf This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 1 (priority 0 sys-id-ext 1) Address fa16.3ed7.dcbf Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Desg FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr Gi0/3 Desg FWD 20000 128.4 Shr Bound(PVST)
  45. 45. MST AND PVST+ ¢ Spanning-tree Switch: Warsaw Warsaw#show spanning-tree vlan 11 MST1 Spanning tree enabled protocol mstp Root ID Priority 1 Address fa16.3ed7.dcbf Cost 20000 Port 2 (GigabitEthernet0/1) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 4097 (priority 4096 sys-id-ext 1) Address fa16.3ee6.4bad Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Root FWD 20000 128.2 Shr Gi0/2 Desg FWD 20000 128.3 Shr
  46. 46. MST AND PVST+ ¢ Spanning-tree Switch: Toronto Toronto#show spanning-tree vlan 11 VLAN0011 Spanning tree enabled protocol ieee Root ID Priority 0 Address fa16.3ee6.4bad Cost 4 Port 4 (GigabitEthernet0/3) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32779 (priority 32768 sys-id-ext 11) Address fa16.3e47.3e34 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Desg FWD 4 128.2 Shr Gi0/2 Desg FWD 4 128.3 Shr Gi0/3 Root FWD 4 128.4 Shr
  47. 47. MST AND PVST+ ¢ Spanning-tree Switch: Montreal Montreal#show spanning-tree vlan 11 VLAN0011 Spanning tree enabled protocol ieee Root ID Priority 0 Address fa16.3ee6.4bad Cost 8 Port 3 (GigabitEthernet0/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32779 (priority 32768 sys-id-ext 11) Address fa16.3e7b.e611 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 300 sec Interface Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- ---------------------- ---------- Gi0/1 Altn BLK 4 128.2 Shr Gi0/2 Root FWD 4 128.3 Shr
  48. 48. MST AND PVST+
  49. 49. MSTP RESTRICTIONS ¢ PVST+, Rapid PVST+, and MSTP are supported, but only one version can be active at any time ¢ VLAN Trunking Protocol (VTP) propagation of the MST configuration is not supported ¢ Partitioning the network into a large number of regions is not recommended ¢ Platform-dependent restrictions
  50. 50. MSTP RESTRICTIONS ¢ Spanning-tree protocols interoperability PVST+ MSTP Rapid PVST+ PVST+ Yes Yes (with restrictions) Yes (reverts to PVST+) MSTP Yes (with restrictions) Yes Yes (reverts to PVST+) Rapid PVST+ Yes (reverts to PVST+) Yes (reverts to PVST+) Yes
  51. 51. MSTP DESIGN CONSIDERATIONS MIGRATION TO 802.1S
  52. 52. MIGRATION TO 802.1S ¢ It’s not possible to convert all of the switches at the same time ¢ So let’s take an advantage of backward compatibility and convert them phase by phase! ¢ Reconfiguration will disrupt the traffic.
  53. 53. MIGRATION TO 802.1S ¢ Step #1 Make proper network documentation! — If you don’t know your network you will break something ¢ Usually when you announce successful migration or you are in bed after long night — Identify ports where BackboneFast and UplinkFast are configured ¢ Those features are PVST+ proprietary — Identify point-to-point and edge ports — Make sure switches are not connected through access link ¢ This may partition the VLAN — Prepare design of MST network topology ¢ Regions ¢ VLAN-s mapping
  54. 54. MIGRATION TO 802.1S ¢ Step #2 Review vendor whitepapers and documentation — There always may be some limitation — There might be things you have to remember during migration due to platform-specific requirements — Something you forgot to prepare or think about might be mentioned there
  55. 55. MIGRATION TO 802.1S ¢ Step #3 Review trunks configuration — Trunks should carry all the VLANs that are mapped to an instance, or — Trunks should not carry any VLANs at all for this instance ¢ Step #4 Ensure that STP is enabled for all VLANs and devices — Do not disable the spanning tree on any VLAN in any of the PVST bridges — Not only switches support STP and require reqconfiguration
  56. 56. MIGRATION TO 802.1S ¢ Step #5 Know your roots — Configure roots on switches that will be roots for particular instance ¢ Easier approach – single root at the beginning, all VLANS mapped to MSTI0 ¢ You will move VLANs to other instances later ¢ That approach require lot work overhead — Set priorities so other switches never become roots
  57. 57. MIGRATION TO 802.1S ¢ Step #6 Start from root, then work your way down — Remember that “new” root MST switch will temporarily block all ports when MST is enabled — Each switch will temporarily block all ports when MST is enabled
  58. 58. MIGRATION TO 802.1S ¢ Step #7 Monitoring — Carefully check STP calculations ¢ Maybe some ports you wanted in Forwarding state are still in Blocking? — Monitor switches resources — Monitor links saturation — Ensure you still have access to core systems in your networks
  59. 59. QUESTIONS?
  60. 60. THANK YOU

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