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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The document discusses the Multiple Spanning Tree Protocol (MSTP) defined by IEEE 802.1s, covering its configurations, operational benefits, and drawbacks in various network scenarios. It emphasizes the protocol's ability to manage multiple VLANs, facilitate network efficiency in multi-vendor environments, and the importance of proper configuration to prevent issues. Additionally, it addresses design considerations, potential pitfalls when integrating MSTP with newer technologies, and includes quizzes for knowledge assessment.
![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](https://image.slidesharecdn.com/piotrwojciechowski-802-161012135016/85/PLNOG-17-Piotr-Wojciechowski-802-1s-MST-czyli-STP-u-operatora-i-w-DC-nie-umarlo-a-nawet-ma-sie-dobrze-w-srodowiskach-multi-vendor-31-320.jpg)
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. IEEE 802.1S, CZYLI STP JESZCZE NIE UMARŁO Piotr Wojciechowski (CCIE #25543)
- 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. 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. 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. MULTIPLE SPANNING TREE PROTOCOL IEEE 802.1S
- 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. 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. 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. A LITTLE BIT OF THEORY OF MST
- 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. MST BPDU
- 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. 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. 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. 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. MSTP DESIGN CONSIDERATIONS VLAN MAPPING
- 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. MSTP DESIGN CONSIDERATIONS SWITCH STACKS
- 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. 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. MSTP DESIGN CONSIDERATIONS MSTP AND NEWER TECHNOLOGIES
- 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. 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)
- 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. 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. 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. 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. 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. MSTP DESIGN CONSIDERATIONS MST AND PVST+
- 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. 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. MST AND PVST+ ¢ Topology Note: ¢ Same VLANs defined on all switches ¢ PVST+ with default STP priorities
- 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. 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. 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. 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. 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. MST AND PVST+
- 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. 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. MSTP DESIGN CONSIDERATIONS MIGRATION TO 802.1S
- 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. 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. 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. 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. 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. 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. 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. QUESTIONS?
- 60. THANK YOU