Dell FTOS 05 Spanning Tree

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

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

5-4

Spanning Tree Protocol Overview

F

F

F

F

F F

F

F

B

B

5-5

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

5-6

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

5-7

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

5-8

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

5-9

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

5-10

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

5-11

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

5-13

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)

5-14

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)

5-15

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




Show spanning-tree 0

View STP information for the chassis

5-16

Force10# show spanning-tree 0 brief


Root ID Priority 32768, Address 0001.e805.7230


Root Bridge hello time 2, max age 20, forward delay 15

Bridge ID Priority 32768, Address 0001.e805.7230


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

5-17

Force10# show spanning-tree 0 interface

Port 1 (TenGigabitEthernet 0/0) of STP 0 is Disable









Port 482 (GigabitEthernet 5/1) of STP 0 is Disable









Force10#

Show spanning-tree 0 interface Use to see interface specific STP information

5-18

Force10# show spanning-tree 0 root

Root ID Priority 32768, Address 0001.e805.7230



Force10#

Show spanning-tree 0 root Use to see specific STP root information

5-19

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

5-20

Layer-2 Protocols




5-21

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

5-22

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

5-23

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

5-24

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

5-25

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

5-26

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

5-27

RSTP: Example

Root

5-28

RSTP: Example

Root

5-29 l

RSTP: Example

Root

5-30

RSTP: Example

Root

5-31

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

5-32 Confidential

Force10# show spanning-tree rstp brief


Root ID Priority 32768, Address 0001.e802.bb7b


Bridge ID Priority 32768, Address 0001.e802.bb7b

We are the root




---------- -------- ---- ------- --- ------- -------------------- ------

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

5-33

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



--------- -------- ---- ------- --- ------- -------------------- ------

--

Po 2 128.3 128 18000 FWD 0 32768 0001.e802.bb7b 128.3

Command: show spanning-tree rstp interface

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


Designated root has priority 32768, address 0001.e802.bb7b

Designated bridge has priority 32768, address 0001.e802.bb7b



BPDU : sent 3628, received 302

The port is not in the Edge port mode

Command: show spanning-tree rstp

5-35

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

5-36

Layer-2 Protocols




5-37

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

5-38

STP: 802.1q Example

VLANs 1-4

VLANs 1-4 VLANs 1-4

5-39

PVST Example

4

3

2

1

4

3

2

1

4

3

2

1

5-40

MSTP: MSTP Example

1,3

2,4

1,3

2,4

1,3

2,4

5-41

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

5-42

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

5-43

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

5-44

MSTP: Regions

5-45

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

5-46

MSTP: IST

IST

5-47

MSTP: IST

5-48

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

5-49

MSTP: MSTI

1,3

2,4

1,3

2,4

1,3

2,4

5-50 Confidential

MSTP: MSTI

MSTI 1 VLANs 1,3

5-51

MSTP: MSTI

MSTI 2 VLANs 2,4

5-52

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)

5-53

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

5-54 l

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

5-55

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

5-56

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

5-57

5. Enable MSTP Globally

By default, MSTP is not enabled in FTOS

Force10(conf)# protocol spanning-tree mstp

Force10(conf-mstp)# no disable

5-58

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

5-59

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


interface gigabitethernet 1/2

switchport

no shutdown



MSTP: Example Configuration Switch A

5-60

Force10# sh spanning-tree msti 1

MSTI 1 VLANs mapped 1, 3

Bridge Identifier has priority 4096, Address 0001.e803.cf63


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


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


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

5-61

Force10# show spanning-tree msti 1 brief

MSTI 1 VLANs mapped 1, 3


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




---------- ------- ---- ------ --- ------ -------------------- -------

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

5-62

Module Summary




Documents

Dell FTOS 05 Spanning Tree