Download - Dell FTOS 05 Spanning Tree
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Dell Force10 Spanning Tree Implementation and Configuration
Module 5
5-2
Objectives Introduction to Spanning Tree
Set Interface Parameters
Layer 2 Protocols
show commands
Debugging
Implementing MSTP
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5-3
FTOS Supports The Following Layer 2 Spanning Tree Protocols
Spanning Tree Protocol (STP)
Rapid Spanning Tree Protocols (RSTP)
Multiple Spanning Tree Protocol (MSTP)
Per VLAN Spanning Tree (PVST) Not covered in this module
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Spanning Tree Protocol Overview
F
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F F
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B
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Spanning Tree Protocol Support
FTOS supports one Spanning Tree instance, per 802.1d standard
Spanning Tree Protocol is disabled by default
When you enable Spanning Tree, all interfaces in L2 mode are added to the Spanning Tree group
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STP Default Values
STG Parameter Default Value
Forward Delay 15 seconds
Hello Time 2 seconds
Max Age 20 seconds
Port Cost
4 = 1-Gigabit Ethernet Interfaces 2 = 10-Gigabit Ethernet Interfaces 3 = Port Channel with 1-Gigabit Ethernet interfaces 1 = Port Channel with 10-Gigabit Ethernet Interfaces 13 = Port Channel with SONET (OC3) interfaces 5 = Port Channel with SONET (OC12) interfaces 14 = SONET interface with speed at 155 (OC3) 6 = SONET interface with speed at 622 (OC12)
Port Priority 8
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STP Configuration
Configuration tasks for Spanning Tree Protocol
Disable STP on any unwanted L2 interfaces
Modify global STP parameters
Set interface parameters
Cost Priority
Portfast
Set STP root bridge selection
1. Enable STP globally
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1. Disable STP on Interfaces
To disable STP on a single port , use the following interface command: Force10 (conf-interface)# no spanning-tree 0
Note: VLAN, Loopback and Null interfaces do not participate in the Spanning Tree topology decisions
Force10# (conf-interface-te-0/0)# show conf
!
interface TenGigabitEthernet 0/0
no ip address
switchport
no spanning-tree 0
no shutdown
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2. Modify Global STP Parameters
The forward-delay, hello-time and max-age parameters configure different BPDU send intervals, and are configurable in protocol spanning-tree mode using these commands:
Force10(conf-span)# forward-delay seconds
Force10(conf-span)# hello-time seconds
Force10(conf-span)# max-age seconds
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3. Set Interface Parameters
Specific port behaviors can be configured from interface mode using these commands:
Force10(conf-interface)# spanning-tree 0 cost cost
Force10(conf-interface)# spanning-tree 0 priority
priority-value
Force10(conf-interface)# spanning-tree 0 portfast
The Portfast feature enables interfaces to begin forwarding packets immediately after they are connected
With Portfast enabled, an interface does not go through the Learning and Listening states and forwards traffic approximately 30 seconds sooner Warning: Enable Portfast only on links connecting to an end
station. Portfast can cause loops if it is enabled on an interface connected to another switched interface
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4. Set STP Root Bridge Selection
In STP, the algorithm determines the root bridge, but you can assign priority to each of the bridges bridge with the lowest number identifier is elected to be the root
To change the bridge priority, use the following command in the PROTOCOL SPANNING TREE mode:
Force10(conf-span)# bridge-priority {priority-value |
primary | secondary}
Primary = 8192
Secondary = 16384
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5. Enable STP Globally
A. There is only one spanning tree supported (Instance 0)
B. To enable STP globally in FTOS, use these commands in the following sequence in configuration mode
Force10(conf)# protocol spanning-tree stp-id
Force10(conf-span)# no disable
C. After you enable the Spanning Tree group, all established VLANs and L2 mode interfaces with no shutdown automatically become part of the Spanning Tree group
D. When STP is enabled the interfaces in L2 mode start sending Bridge Protocol Data Units (BPDU)
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5. Enable STP Globally
A. There is only one spanning tree supported (Instance 0)
B. To enable STP globally in FTOS, use these commands in the following sequence in configuration mode
Force10(conf)# protocol spanning-tree stp-id
Force10(conf-span)# no disable
C. After you enable the Spanning Tree group, all established VLANs and L2 mode interfaces with no shutdown automatically become part of the Spanning Tree group
D. When STP is enabled the interfaces in L2 mode start sending Bridge Protocol Data Units (BPDU)
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Force10# show spanning-tree 0
Executing IEEE compatible Spanning Tree Protocol
Bridge Identifier has priority 32768, address 0001.e805.7230
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Current root has priority 32768, address 0001.e805.7230
Topology change flag not set, detected flag not set
Timers: hold 1, topology change 35
hello 2, max age 20, forward delay 15
Times: hello 1, topology change 0, notification 0, aging Normal
Port 1 (TenGigabitEthernet 0/0) is Disabled
Port path cost 2, Port priority 8, Port Identifier 8.1
Designated root has priority 32768, address 0001.e805.7230
Designated bridge has priority 32768, address 0001.e805.7230
Designated port id is 8.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state 0
BPDU: sent 0, received 0
The port is not in the portfast mode
Port 482 (GigabitEthernet 5/1) is Disabled
Port path cost 4, Port priority 8, Port Identifier 8.482
Designated root has priority 32768, address 0001.e805.7230
Designated bridge has priority 32768, address 0001.e805.7230
Show spanning-tree 0
View STP information for the chassis
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Force10# show spanning-tree 0 brief
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 32768, Address 0001.e805.7230
We are the root of the spanning tree
Root Bridge hello time 2, max age 20, forward delay 15
Bridge ID Priority 32768, Address 0001.e805.7230
Configured hello time 2, max age 20, forward delay 15
Interface Designated
Name PortID Prio Cost Sts Cost Bridge ID PortID
-------------- ------ ---- ---- --- ----- ----------------- ------
Te 0/0 8.1 8 2 DIS 0 32768 0001.e805.7230 8.1
Gi 5/1 8.482 8 4 DIS 0 32768 0001.e805.7230 8.482
Force10#
Show spanning-tree 0 brief
View a snapshot of chassis state its interface configuration
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Force10# show spanning-tree 0 interface
Port 1 (TenGigabitEthernet 0/0) of STP 0 is Disable
Port path cost 2, Port priority 8, Port Identifier 8.1
Designated root has priority 32768, address 0001.e805.7230
Designated bridge has priority 32768, address 0001.e805.7230
Designated port id is 8.1, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state 0
BPDU: sent 0, received 0
The port is not in the portfast mode
Port 482 (GigabitEthernet 5/1) of STP 0 is Disable
Port path cost 4, Port priority 8, Port Identifier 8.482
Designated root has priority 32768, address 0001.e805.7230
Designated bridge has priority 32768, address 0001.e805.7230
Designated port id is 8.482, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state 0
BPDU: sent 0, received 0
The port is not in the portfast mode
Force10#
Show spanning-tree 0 interface Use to see interface specific STP information
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Force10# show spanning-tree 0 root
Root ID Priority 32768, Address 0001.e805.7230
We are the root of the spanning tree
Root Bridge hello time 2, max age 20, forward delay 15
Force10#
Show spanning-tree 0 root Use to see specific STP root information
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Force10# show spanning-tree 0 summary
Root bridge for Spanning Tree 0 is this bridge
Rapid root failover is disabled
State Blocking Listening Learning Forwarding STP Active
Num of Ports 0, 0, 0, 3, 3
Force10#
Show spanning-tree 0 summary Use to see a summary of the system STP information
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Layer-2 Protocols
Spanning Tree Protocol (STP)
Rapid Spanning Tree Protocols (RSTP)
Multiple Spanning Tree Protocol (MSTP)
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Rapid Spanning-Tree Protocol
Standardized protocol, 802.1w Functionally similar to Spanning-Tree Protocol (STP)
Both will generate the same topology but RSTP will converge much faster
Interoperable with STP and MSTP
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RSTP: States and Roles are Different
RSTP merges states from STP RSTP adds additional roles to STP
STP States RSTP States
Forwarding
Learning
Listening
Blocking
Disabled
Forwarding
Learning
Discarding
STP Roles RSTP Roles
Root
Designated
Root
Designated
Alternate
Backup
Edge
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RSTP Port Roles Those that FORWARD
Root Port The port that is the closest to the root
bridge based on path cost, a bridge sends traffic on this port to the root
Designated Port The port that is the closest to the root
bridge based on path cost, a bridge receives traffic on this port from others on the segment
Those that DONT Forward Alternate Port
A port that is an alternate path to the root on a different bridge than the designated bridge
Backup Port A port that is an alternate path to the root
on the designated bridge Disabled Port
A port that has no role in RSTP
D D
D
Root Bridge
R R
A B
X X
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RSTP Port Costs
Link Speed STP (802.1d)
Default Port Costs RSTP (802.1w)
Default Port Costs
100M 19 200000
1G 4 20000
10G 2 2000
100M LAG 18 180000
1G LAG 3 18000
10G LAG 1 1800
Default port costs have changed
Be aware of this when running RSTP with STP compatibility
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RSTP: BPDUs
New BPDU format New Type 2 and version 2 so .1D bridges must drop PDU
Expanded use from 802.1d Spanning Tree BPDU All bits of flags now used to communicate additional state Version 1 only used topology change bits (0 & 7)
BPDUs sent every seconds (2 by default) Even if it does not receive BPDUs from the root bridge
Acts as keep alive between bridges Allows much faster failure detection
Topology Change
Topology Change
ACK
0 1 2 3 4 5 6 7
RSTP Flag Byte
Proposal Port Role Learning Forwarding Agreement
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RSTP: Why Rapid?
STP
based on timers to allow BPDUs to
flow from root to all leaves
stays a set time in listening and
learning modes to gather all
available BPDU information to
decide port state
RSTP
uses BPDUs as keepalives between adjacent switches
establishes state before passing information to the downstream device
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RSTP: Example
Root
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RSTP: Example
Root
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RSTP: Example
Root
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RSTP: Example
Root
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RSTP Configuration
1. Disable STP on any unwanted L2 interfaces 2. Modify other global bridge settings (bridge-priority, forward-delay, hello-
time, max-age)
3. Set interface parameters a) Cost
b) Priority c) Portfast
4. Configure edge ports, if needed Force10(conf)# interface g0/1
Force10(conf-interface-gi-0/1)# spanning-tree rstp
edge-port
If a port is in edge-port mode it will behave as a normal port if a BPDU is received
5. Enable RSTP globally, it will then run on all L2 ports Force10(conf)# protocol spanning-tree rstp
Force10(conf-rstp)# no disable
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Force10# show spanning-tree rstp brief
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 32768, Address 0001.e802.bb7b
Root Bridge hello time 2, max age 20, forward delay 15
Bridge ID Priority 32768, Address 0001.e802.bb7b
We are the root
Configured hello time 2, max age 20, forward delay 15
Interface Designated
Name PortID Prio Cost Sts Cost Bridge ID PortID
---------- -------- ---- ------- --- ------- -------------------- ------
Po 2 128.3 128 18000 FWD 0 32768 0001.e802.bb7b 128.3
Po 5 128.6 128 18000 FWD 0 32768 0001.e802.bb7b 128.6
Interface
Name Role PortID Prio Cost Sts Cost Link-type Edge
---------- ------ -------- ---- ------- --- ------- --------- ----
Po 2 Desg 128.3 128 18000 FWD 0 P2P No
Po 5 Desg 128.6 128 18000 FWD 0 P2P No
Command: show spanning-tree rstp brief
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Force10# show spanning-tree rstp interface port-channel 2
Port-channel 2 is designated forwarding
Edge port:no (default) port guard :none (default)
Link type: point-to-point (auto) bpdu filter:disable (default)
Bpdu guard :disable (default)
Bpdus sent 3502, received 269
Interface Designated
Name PortID Prio Cost Sts Cost Bridge ID PortID
--------- -------- ---- ------- --- ------- -------------------- ------
--
Po 2 128.3 128 18000 FWD 0 32768 0001.e802.bb7b 128.3
Command: show spanning-tree rstp interface
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5-34 Confidential
Force10# show spanning-tree rstp
Root Identifier has priority 32768, Address 0001.e802.bb7b
Root Bridge hello time 2, max age 20, forward delay 15, max hops 0
Bridge Identifier has priority 32768, Address 0001.e802.bb7b
Configured hello time 2, max age 20, forward delay 15, max hops 0
We are the root
Current root has priority 32768, Address 0001.e802.bb7b
Number of topology changes 78, last change occured 03:38:08
Port 3 (Port-channel 2) is designated Forwarding
Port path cost 18000, Port priority 128, Port Identifier 128.3
Designated root has priority 32768, address 0001.e802.bb7b
Designated bridge has priority 32768, address 0001.e802.bb7b
Designated port id is 128.3, designated path cost 0
Number of transitions to forwarding state 74
BPDU : sent 3628, received 302
The port is not in the Edge port mode
Command: show spanning-tree rstp
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Force10# debug spanning-tree rstp ?
all RSTP all debug
bpdu RSTP debug BPDU
events RSTP debug events
RSTP Debugging Many debug options to trace RSTP PDUs and events
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Layer-2 Protocols
Spanning Tree Protocol (STP)
Rapid Spanning Tree Protocols (RSTP)
Multiple Spanning Tree Protocol (MSTP)
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Multiple Spanning-Tree Protocol (802.1s)
802.1q standard specified only one Spanning-Tree Instance for all VLANs
Many vendors provide separate Spanning-Tree Instance for every VLAN Uses too much CPU time and sends too many BPDUs to be scalable
MSTP uses the best of both systems to create a flexible and scalable solution Creates a finite number of Spanning-Tree Instances and maps each of
the VLANs in the networks to one of the Instances Allows for all segments to be utilized while only requiring a few Instances
of the Spanning-Tree Algorithm Uses RSTP as its convergence algorithm
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STP: 802.1q Example
VLANs 1-4
VLANs 1-4 VLANs 1-4
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PVST Example
4
3
2
1
4
3
2
1
4
3
2
1
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MSTP: MSTP Example
1,3
2,4
1,3
2,4
1,3
2,4
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MSTP: BPDUs
There is only one MSTP Instance that sends and receives MSTP BPDUs
The other Instance information is encapsulated in the MSTP BPDUs Similar to Per VLAN Spanning Tree
Limits the number of BPDUs to 1 instead of to the number of VLANs
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MSTP: Definitions
MST Region Contiguous group of switches that share the same MSTP
configuration
Common Spanning-Tree (CST)
The Spanning-Tree Instance external to the region
Internal Spanning-Tree (IST) Special Spanning-Tree Instance that interacts with the CST
MST Instance (MSTI)
These are the Spanning-Tree Instances used internal to a region that the VLANs are mapped to
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MSTP: Regions
Each MSTP Region is configured with A mapping of VLANs to MSTIs -
mandatory
Name (*optional) Revision number (*optional)
When a switch is connected to another switch with different characteristics, it is considered to be in another Region
Whenever possible, all switches in the network should be in the same Region
*Every switch in the Region must be configured with these exact same 3 values
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MSTP: Regions
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MSTP: IST
The IST is important because this is the Instance that interacts with the CST
The IST allows the Region to appear to the CST as a single switch
This allows MSTP to interoperate with legacy environments
The IST is also present internal to the region VLANs can be mapped to the IST, but in general should not be
The IST is the Instance that sends and receives BPDUs
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MSTP: IST
IST
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MSTP: IST
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MSTP: MSTI
The MSTIs are all internal to the Region
All VLANs in the region will be mapped to one of the MSTIs Each Region can support up to 64 MSTIs, although in practice, only two or
three are usually necessary
There are not separate BPDUs for each MSTI
A BPDU sent between two switches contains information about all of the MSTIs
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MSTP: MSTI
1,3
2,4
1,3
2,4
1,3
2,4
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MSTP: MSTI
MSTI 1 VLANs 1,3
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MSTP: MSTI
MSTI 2 VLANs 2,4
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MSTP: Basic Configuration Steps
1. Map VLANs to Instances (mandatory)
2. Modify global MSTP parameters (optional)
3. Disable MSTP on interfaces (optional)
4. Set MSTP interface parameters (optional)
5. Enable MSTP globally (mandatory)
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1. MSTIs to VLAN Mapping
All VLANs are mapped to Instance 0 when MSTP is enabled Instance 0 can not be used to carry internal VLAN information
To change the VLAN mapping use the following command in MSTP mode:
Force10(conf-mstp)# msti vlan
Note all mappings must be the same on every router in the region
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2. Modify Global MSTP Parameters (optional) The following MSTP parameters can be modified in MSTP configuration
mode: Forward-delay
Hello-timer Max-age
Max-hop Bridge-priority (per MSTI)
Force10(conf-mstp)# msti bridge-priority
* Name Force10(conf-mstp)# name
* Revision Force10(conf-mstp)# revision
* If Name and Revision are configured they must be the same on every router in the region
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3. Disable MSTP on interfaces (optional)
When MSTP is enabled globally, every layer-two interface is automatically enabled in MSTP
Layer-three interfaces are not enabled in MSTP
To disable MSTP: Force10(conf-interface)# no spanning-tree
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4. Modify MSTP Interface Parameters
On each interface, the cost and priority for MSTP can be modified with the following interface commands:
Force10(conf-interface)# spanning-tree msti cost
Force10(conf-interface)# spanning-tree msti
priority
To make an interface an edge-port, use the following command in interface mode:
Force10(conf-interface)# spanning-tree mstp edge-port
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5. Enable MSTP Globally
By default, MSTP is not enabled in FTOS
Force10(conf)# protocol spanning-tree mstp
Force10(conf-mstp)# no disable
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MSTP: Example
MSTI 1 VLANs 1,3
MSTI 2 VLANs 2,4
Switch A Switch B
Switch C
1/1
1/2
3/1 3/2
2/1
2/2
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protocol spanning-tree MSTP
no disable
msti 1 vlan 1,3
msti 2 vlan 2,4
name labmstp1
revision 1
msti 1 bridge-priority 4096
interface gigabitethernet 1/1
switchport
no shutdown
spanning-tree msti 1 priority 112
spanning-tree msti 2 priority 112
interface gigabitethernet 1/2
switchport
no shutdown
spanning-tree msti 1 priority 112
spanning-tree msti 2 priority 224
MSTP: Example Configuration Switch A
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Force10# sh spanning-tree msti 1
MSTI 1 VLANs mapped 1, 3
Bridge Identifier has priority 4096, Address 0001.e803.cf63
Configured hello time 2, max age 20, forward delay 15, max hops 20
Current root has priority 4096, Address 0001.e803.cf63
Number of topology changes 7, last change occured 21:39:18
Port 82 (GigabitEthernet 1/1) is designated Forwarding
Port path cost 20000, Port priority 112, Port Identifier 112.82
Designated root has priority 4096, address 0001.e803.cf:63
Designated bridge has priority 4096, address 0001.e803.cf:63
Designated port id is 112.82, designated path cost
Number of transitions to forwarding state 2
BPDU (Mrecords): sent 4229, received 7941
The port is not in the Edge port mode
Command: show spanning-tree msti Shows a particular MSTI and the interfaces configured in it
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Force10# show spanning-tree msti 1 brief
MSTI 1 VLANs mapped 1, 3
Executing IEEE compatible Spanning Tree Protocol
Root ID Priority 4096, Address 0001.e803.cf63
Root Bridge hello time 2, max age 20, forward delay 15, max hops 20
Bridge ID Priority 4096, Address 0001.e803.cf63
Configured hello time 2, max age 20, forward delay 15, max hops 20
Interface Designated
Name PortID Prio Cost Sts Cost Bridge ID PortID
---------- ------- ---- ------ --- ------ -------------------- -------
Gi 1/1 112.82 112 20000 FWD 0 4096 0001.e803.cf63 112.82
Gi 1/2 112.88 112 20000 FWD 0 4096 0001.e803.cf63 112.88
Interface
Name Role PortID Prio Cost Sts Cost Link-type
---------- ------ ------- ---- ------ --- ------ -----------
Gi 1/1 Desg 112.82 112 20000 FWD 0 P2P
Gi 1/2 Desg 112.88 112 20000 FWD 0 P2P
Command: show spanning-tree mstp brief Shows a particular MSTI and the interfaces configured in it in a tabular format
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Module Summary
Spanning Tree Protocol (STP)
Rapid Spanning Tree Protocols (RSTP)
Multiple Spanning Tree Protocol (MSTP)