Wired Networks

Global MSTP Configuration on MAS

Introduction- For Layer 2 loop-prevention, S3500 supports Multiple Spanning-tree Protocol (MSTP) at FCS. Also referred as IEEE 802.1s, where it was originally defined.
MSTP is extension to Rapid Spanning-tree Protocol (RSTP). MSTP provides added benefit from RSTP (and STP) by allowing individual VLANs to be mapped to instance(s).
All VLANs are no longer forced to be on the same logical topology. Can reduce un-utilized links and allow load-balancing.
Common Spanning-tree Instance (CST): All VLANs are forced to map to same logical topology. Load-balancing is not allowed  resulting un-utilized links
VLANs mapping to MST instances:

  • Better resource utilization where multiple VLANs can be mapped to instances. Load balancing can be allowed to utilize all links.

MSTP – Regions
MSTP Region is a group of switches running MSTP with same parameters:

  • Region name
  • Revision number
  • VLAN-to-instance mapping
  • The BPDUs containing MST instance(s) information do not traverse beyond the region
  • Must ensure the parameters are identical to be placed in the same region
  • Maximum 64 instances – one regional root bridge per instance
  • The instance 0 (Internal Spanning Tree/IST) is special instance where all VLANs belong by default and carries all STP related information.
  • Single spanning-tree across all MST regions - Common Spanning-tree (CST).

MSTP – RSTP/STP Interoperability           

  • MSTP is backward-compatible with RSTP and STP.
  • Each MST Regions will simply appear as transparent virtual bridge.
  • Common and Internal Spanning Tree (CIST) extends CST into the region.

Configuration Steps- MSTP can be configured under global MSTP configuration:
(ArubaS3500) (config) #mstp
(ArubaS3500) (Global MSTP) #region-name MSTP_REGION_A
(ArubaS3500) (Global MSTP) #instance 0 bridge-priority 61440
(ArubaS3500) (Global MSTP) #instance 1 bridge-priority 61440
(ArubaS3500) (Global MSTP) #instance 1 vlan 100
(ArubaS3500) (Global MSTP) #instance 2 bridge-priority 61440
(ArubaS3500) (Global MSTP) #instance 2 vlan 200
(ArubaS3500) (Global MSTP) #revision <number>
Bridge-priority must increment in terms of 4096 (4K).
Accepted values are: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, etc. Default is 32768.
MSTP – Interface-profile
MSTP path cost and priority values can be configured under MSTP interface-profile:
(ArubaS3500) (config) #interface-profile mstp-profile MSTP_A
(ArubaS3500) (Interface MSTP "MSTP1") #instance 1 cost 20000
(ArubaS3500) (Interface MSTP "MSTP1") #instance 1 priority 128
(ArubaS3500) (Interface MSTP "MSTP1") #point-to-point
Path-priority must increment in terms of 16.
Configured MSTP interface-profile then needs to be applied to the interface:
(ArubaS3500) (config) #interface gigabitethernet 0/0/2
(ArubaS3500) (gigabitethernet "0/0/2") #mstp-profile MSTP_A
MSTP - Verification
MSTP configuration can be verified using following CLI command:
(ArubaS3500) #show mstp-global-profile
Global MSTP
Parameter                 Value
---------                 -----
Enable MSTP protocol      Enabled
MSTP region name          MSTP_REGION_A
MSTP revision             0
Instance bridge priority  0 61440
Instance bridge priority  1 61440
Instance bridge priority  2 61440
Instance vlan mapping     1 100
Instance vlan mapping     2 200
MSTP hello time           2
<output truncated>
MSTP – Operation Verification
MSTP operation can be verified using following CLI command:
(ArubaS3500) #show mstp msti all
vlans mapped: 1 2 3 4
Root      address 000b.866a.2ac0  priority 0xf000
Bridge    address 000b.866a.2ac0  priority 0xf000
Interface              Role  State  Port Id  Cost    Type
---------              ----  -----  -------  ----    ----
gigabitethernet0/0/2   Desg  FWD    128.3    20000   P2p
gigabitethernet0/0/3   Desg  FWD    128.4    20000   P2p
<output truncated>
MSTP – Interface Verification
MSTP interface can be verified using following CLI command:
(ArubaS3500) #show mstp interface gigabitethernet 0/0/2 detail
Port 3 (gigabitethernet0/0/2) of MST 0 is designated forwarding
Port path cost 20000, Port priority 128, Port Identifier 128.3
Designated root has priority 0xf000, address 000b.866a.2ac0
Designated bridge has priority 0xf000, address 000b.866a.2ac0
Number of transitions to forwarding state: 2
Link type is point-to-point by default, Internal
BPDU: sent 110, received 0
<output truncated>



Version History
Revision #:
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Last update:
‎04-05-2015 06:17 AM
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