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© 2003 Hewlett-Packard Development Company, L.P.The information contained herein is subject to change without notice

DECUS IT-Symposium 2006

Spanning Tree ProtocolInteroperability Cisco/HP ProCurve

Juergen BrunsNetwork Competency Center EMEA

HP Services

page 2May 17, 2006

Agenda

• Protocol refresh• IEEE802.1D• PVST+• IEEE802.1w• IEEE802.1s• Cisco STP• ProCurve STP• Configuration Example

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page 3May 17, 2006

Requirements for a Layer 2 redundancy protocol

• Provide a loopfree topology, meaning a packet should never be seen twice in a network

• Only ONE active path between two hosts• Should activate redundant links in case of a failure• Convergence time should be as quick as possible• Nice to have: Utilize redundant links

page 4May 17, 2006

Preventing Bridging Loops

Station A

Station B

2/2

2/11/1

1/2

Segment A

Segment B

Neither Switch A or Brunning STP

2

4

7

1

3

6

5

2

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page 5May 17, 2006

Preventing Bridging Loops

Bridging loops can be prevented by disabling theredundant path

Station A

Station B

2/2

2/11/1

1/2

Segment A

Segment B

page 6May 17, 2006

STP and IEEE Standards

• The First IEEE standard implementation of STP is IEEE 802.1D. (since 1998)

• RSTP is Rapid Spanning-Tree Protocol defined by the IEEE 802.1w. (since 2001)

• MSTP is Multiple Spanning-Tree Protocol defined by the IEEE 802.1s. (since 2002/2003, Standard Compliance on Cisco since 2006)

Cisco proprietär• PVST is Per VLAN Spanning-tree proprietary implementation of STP

on Cisco equipment using a ISL trunk.• (Rapid) - PVST+ is the implementation of PVST on 802.1q links. • IEEE 802.1s Vlan MST based on a pre-standards draft.

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page 7May 17, 2006

STP – Calculating a loop free network

1. Select the Root bridge=> lowest Bridge ID (Bridge Prio + Bridge Mac)

2. Select Root ports, 1 per Bridge=> shortest path to root

3. Select Designated port, 1 per Segment => shortest path to root=> Lowest Sender Bridge ID used as tie-breaker

4. Use Port ID as tie-breaker=> lowest Port ID (Port Prio + System #)

page 8May 17, 2006

Which port is blocking ?

Gbit/s

Switch C

Switch A

Switch B

• Brigde MAC (A=x1, B=x2, C=x3)• Bridge Prio (default: 32768)• Port cost (default: Gbit/s=4, 100Mbit/s=19)• Path cost (sum of all port costs to root)• Port priority (default = 32)

Gbit/s

100 Mbit/s

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page 9May 17, 2006

802.1D root bridge election

The Bridge/Switch having the lowest Bridge ID is the Root BridgeThe Bridge Priority, default to 32768, is configurable.

Bridge ID

Priority MAC Address

00010800ABCD012100010800ABCD0121

6 bytes6 bytesBPDUs

Root Bridge

2 bytes2 bytes

80000800102031DE80000800102031DE

80000800102032AC80000800102032AC

80000800102034238000080010203423

8000080010203EF888000080010203EF88

page 10May 17, 2006

802.1D root port election

Each bridge retains the lowest cost to reach the Root bridge, on each port.The best port (Root Port) is then elected:

1010 1010

10101010

1010

2020

2020

3030

30301010Link Cost

Root Port

2020

3030

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page 11May 17, 2006

802.1D designated port

For each segment, only the best path is used towards the Root Bridge.The corresponding port is called the Designated Port (DP) .Redundant Bridges are blocked.

1010 1010

10101010

1010 2020

2020

3030

30301010

Hub

DPDP DPDP

DPDP DPDP

DPDPDPDP

DPDP

DPDP

DPDP

DPDP

Cost=0

DPDPDPDP

AA

BB

page 12May 17, 2006

802.1D logical topology

Topology becomes loopfree

Hub

AA

BB

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page 13May 17, 2006

802.1D and 802.1t

802.1D port costs (16 Bit)

1 to 65535 4 1 Gbps

1 to 65535 19 100 Mbps

1 to 65535 100 10 Mbps

Default Range Default Cost Value Port Speed

1 to 200000000 200 to 20000 2000 10 Gbps

1 to 200000000 2000 to 200000 20000 1 Gbps

1 to 200000000 20000 to 2000000 200000 100 Mbps

1 to 200000000 200000 to 20000000 2000000 10 Mbps

1 to 200000000 2000000 to 200000000 20000000 1 Mbps

1 to 200000000 20000000 to 200000000 200000000 > 100 kbps

Available Range Recommended Range Recommended Value Port Speed

802.1t port costs (32 Bit) used for IEEE 802.1w and IEEE 802.1s

page 14May 17, 2006

Per VLAN Spanning Tree (PVST+)

• Cisco‘s implementation of STP• Cisco switches run per-VLAN Spanning tree • Each VLAN builds its own STP instance (<128)• Provides loadbalancing

• No standard, but compatible with 802.1D• CST BPDUs are send untagged in VLAN1, even ifthe native VLAN is not = VLAN 1

• Shared Spanning Tree BPDUs are sent tagged foreach VLAN (exept for the native VLAN) to MAC: 0100.0ccc.cccd

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page 15May 17, 2006

PVST+ Loadbalancing

Sample Topology for VLAN 10:

Hub

AA

BB

page 16May 17, 2006

PVST+ Loadbalancing

Sample Topology for VLAN 20:

Hub

AA

BB

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page 17May 17, 2006

802.1D protocol states

Time

Blocking

20 SecListening

Learning15 Sec

Forwarding

15 Sec

Forward Delay

Forward Delay

Max-Age

page 18May 17, 2006

Rapid Spanning Tree 802.1w Overview

• Extension to 802.1D => higher convergence speed.• Includes features similar to UplinkFast, Backbone Fast and

PortFast.• New Port Role• Modified BPDU• Rapid port state transition.• New topology change mechanism.• 802.1D Compatibility• IEEE 802.1w - a standard since June 2001.• Rapid PVST+ has the same architecture as PVST+ except that it uses 802.1W rapid STP protocol instead of 802.1D

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page 19May 17, 2006

802.1w port roles

4 port roles

• Root port: shortest path to the root bridge in terms of pathcosts (Forwarding)

• Designated port: the port which is sending the best PBDUfor a segment (Forwarding)

• Alternate Port: an port which has an alternative path to the root bridge (Blocking = Discarding)

• Backup Port: Port which has link to the same segment on the same switch (Blocking = Discarding)

page 20May 17, 2006

802.1w port roles

Hub

AA

BB

RPRP

DPDP

RPRP

BPBP

DPDP

Port rolesRP = Root portDP = Designated PortAP = Alternate PortBP = Backup Port

APAP

APAP

HUB

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page 21May 17, 2006

Multi Instance Spanning Tree IEEE 802.1s Features

The latest Spannng Tree standard

• Fast convergence

• Can make use of all links in network

• Makes STP scalable

page 22May 17, 2006

802.1s

Before (802.1D or 802.1w)

VLANs 1VLANs 2

VLANs 1VLANs 2

RootVLANs 3

VLANs 3

VLANs 1VLANs 2

VLANs 3

Before (with PVST)

Root of 1

VLANs 1VLANs 2

VLANs 3

VLANs 1VLANs 2

VLANs 3Root of 2

Root of 3

VLANs 1VLANs 2

VLANs 3

Now with 802.1s

MSTI-1 Root MSTI-2 Root

VLANs 1,2…VLAN 3,4…

VLANs 1,2…VLAN 3,4…

VLANs 1,2…VLAN 3,4…

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page 23May 17, 2006

802.1s Terms

• MST Region: a group of switches running 802.1s undercommen set of configuration attributes

• MST instance: an entity which will calculate his owntopology. Each instance can be used for one or moreVLANs

• Common Spanning Tree (CST): An STP or RSTP spanningtree instance to interconnect differrent regions

• Internal Spanning Tree (IST): RSTP instance interconnectingCST to the region. All ohter VLANs that are not configured

manualy to an instance are mapped automatically to the IST = MST Instance 0.

page 24May 17, 2006

802.1s Terms

MSTRegion IST

CST

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page 25May 17, 2006

MSTP - Configuring Regions - ProCurve

MSTP - Configuring Regions for ProCurve

To create multiple spanning tree instances, an MST "region" is

defined, with 3 parameters that must be identical for each switch

in the region:

• region name ("spanning-tree config-name")

• revision number ("spanning-tree config-revision")

• VLAN-to-instance mapping ("span instance <1-16> vlan <VID>")

Each VLAN can be a member of only 1 MST instance.

Any VLANs not claimed by (not configured in) an MST instance

automatically exist in instance 0 (the Internal Spanning Tree, or

IST), which always exists when MSTP is enabled.

page 26May 17, 2006

Summary and Guide-line

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page 27May 17, 2006

Cisco vs ProCurve STP Protocols

Cisco IOS switch can run the following protocols:

• Common Spanning Tree (IEEE 802.1D)

• PVST+

• Rapid PVST+ (default)

• MSTP IEEE 802.1s draft

• MSTP IEEE 802.1s Standard Compliance

ProCurve Switch can enable the following protocols:

• Common Spanning Tree (IEEE 802.1D)

• PVST+ (only 9300 Series)

• Rapid STP (IEEE 802.1w) per box (default)

• MSTP IEEE 802.1s Standard Compliance

page 28May 17, 2006

Interoperability Cisco & ProCurve

• Try to use the MSTP IEEE802.1s Standard Compliance Version on Cisco and enable MSTP on ProCurve

• Try to build at least one region. It will act as a virtual bridge.

• Between the regions or to other STP Bidges the "Common Spanning Tree" (CST) is the active tree.

• In IEEE802.1s the CST can use Rapid STP or the older version .1D

• When connection a MST Region to (rapid) - PVST+ device be awarethat the CST is running untagged on VLAN1 regardless of the native vlan.

• Check the STP cost setting when connecting a IEEE802.1s or. 1w configuration to a Cisco Rapid PVST+ or .1D bridge. You can revertthe cost on ProCurve to the legacy settings.

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page 29May 17, 2006

Cisco MSTP IEEE 802.1s Standard Compliance

Device Required IOSCisco Catalyst2950, 3550, IOS 12.2(25)SEC3560, 3750

Cisco Catalyst IOS 12.2(25)SG4000 No CatOS version

Cisco Catalyst IOS 12.2(18)SXF6000 or CatOS 8.3

Please refer to Cisco Website and select the Software Advisor Tool

http://www.cisco.com/public/support/tac/tools.shtml

page 30May 17, 2006

Example Configuring MSTP on ProCurve/Cisco

Sample topology

Parameters for the MSTP are as follows:

Config Name: hp-ciscoConfig Revision #: 1Instance 1 VLAN 1,10,20Instance 2 VLAN 30,40

Cisco-1 is Root for instances 0 (IST) and 1

Cisco-2 is Root for instance 2

HP ProCurve switches, ProCurve-Edge-1 and 2, are defined as edge switches

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page 31May 17, 2006

Configuring MSTP on Cisco

The Cisco Switch 1 is defined as Root for instances 0 (IST) and 1, and secondary Root for instance 2.

Conf t

hostname Cisco-1Spanning-Tree mode mstSpanning-Tree extend system-id!Spanning-Tree mst configurationname hp-ciscorevision 1instance 1 vlan 1, 10, 20instance 2 vlan 30, 40

Spanning-Tree mst 0-1 priority 0Spanning-Tree mst 2 priority 4096end

The Cisco Switch 2 is defined as Root for instances 2 and secondary Root for instance 0 and 1.

Conf thostname Cisco-2Spanning-Tree mode mstSpanning-Tree extend system-id!Spanning-Tree mst configurationname hp-ciscorevision 1instance 1 vlan 1, 10, 20instance 2 vlan 30, 40

!Spanning-Tree mst 0-1 priority 4096Spanning-Tree mst 2 priority 0

page 32May 17, 2006

Configuring MSTP on ProCurve

ProCurve-Edge-1 and 2 are defined as edge switches.

hostname "ProCurve-Edge-1/2" Spanning-TreeSpanning-Tree protocol-version MSTP

Spanning-Tree config-name "hp-cisco"Spanning-Tree config-revision 1Spanning-Tree instance 1 vlan 1 10 20Spanning-Tree instance 2 vlan 30 40

Cisco-1#sh span mst configuration Name [hp-cisco]Revision 1Instance Vlans mapped-------- -------------------------------------------------------------0 2-9,11-19,21-29,31-39,41-40941 1,10,202 30,40-----------------------------------------------------------------------

Result

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page 33May 17, 2006

Useful Cisco Troubleshooting Commands

CatOS IOSsh spant summary sh spann summary (summary of features / ports)

sh spant <vlan> active sh spann vlan <vlan> detail(STP state for a vlan)

sh spant mst [inst] sh spann mst [inst] (STP state for MST instance)

sh spant <mod/port> sh spann int <int> detail (STP state for port)

sh spant stat <mod/port> <vlan> sh span int <int> detail

page 34May 17, 2006

Summary

• Create a STP Design, Test and Implementation Plan

• Try to use the IEEE 802.1s Standard Compliance Version

• Check the lastest FW or IOS versions

• Check the Common Spanning Tree settings

• When using PVST+ take care for VLAN1

• If the STP is stable, secure it using BPDU Guard, Root Guard…

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