DECUS IT-Symposium 2006 Spanning Tree Protocol Interoperability Cisco/HP ProCurve Juergen Bruns Network Competency Center EMEA HP Services 2003 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice Agenda Protocol refresh IEEE802.1D PVST+ IEEE802.1w IEEE802.1s Cisco STP ProCurve STP Configuration Example page 2 1
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 3 Preventing Bridging Loops Neither Switch A or B running STP Station A 1 5 6 1/1 2 2 2/1 Segment A 1/2 3 2/2 4 7 Segment B Station B page 4 2
Preventing Bridging Loops Bridging loops can be prevented by disabling the redundant path Station A Segment A 1/1 2/1 1/2 Segment B 2/2 Station B page 5 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. page 6 3
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 7 Which port is blocking? Switch A Gbit/s Gbit/s Switch B 0 Mbit/s Brigde MAC (A=x1, B=x2, C=x3) Bridge Prio (default: 32768) Port cost (default: Gbit/s=4, 0Mbit/s=19) Path cost (sum of all port costs to root) Port priority (default = 32) Switch C page 8 4
802.1D root bridge election The Bridge/Switch having the lowest Bridge ID is the Root Bridge The Bridge Priority, default to 32768, is configurable. Root Bridge 000800ABCD0121 800008002031DE 80000800203423 BPDUs 2 bytes 6 bytes 800008002032AC 80000800203EF88 Priority Bridge ID MAC Address page 9 802.1D 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: 20 20 30 30 30 20 Root Port Link Cost page 5
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 (). Redundant Bridges are blocked. Cost=0 A 30 20 30 20 Hub B page 11 802.1D logical topology Topology becomes loopfree Hub A B page 12 6
802.1D and 802.1t 802.1D port costs (16 Bit) Port Speed Mbps 0 Mbps 1 Gbps Default Cost Value 0 19 4 Default Range 1 to 65535 1 to 65535 1 to 65535 802.1t port costs (32 Bit) used for IEEE 802.1w and IEEE 802.1s Port Speed Recommended Value Recommended Range Available Range > 0 kbps 200000000 20000000 to 200000000 1 to 200000000 1 Mbps 20000000 2000000 to 200000000 1 to 200000000 Mbps 2000000 200000 to 20000000 1 to 200000000 0 Mbps 200000 20000 to 2000000 1 to 200000000 1 Gbps 20000 2000 to 200000 1 to 200000000 Gbps 2000 200 to 20000 1 to 200000000 page 13 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 if the native VLAN is not = VLAN 1 Shared Spanning Tree BPDUs are sent tagged for each VLAN (exept for the native VLAN) to MAC: 00.0ccc.cccd page 14 7
PVST+ Loadbalancing Sample Topology for VLAN : Hub A B page 15 PVST+ Loadbalancing Sample Topology for VLAN 20: Hub A B page 16 8
802.1D protocol states Time 20 Sec 15 Sec 15 Sec Blocking Max-Age Listening Forward Delay Learning Forward Delay Forwarding page 17 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 page 18 9
802.1w port roles 4 port roles Root port: shortest path to the root bridge in terms of path costs (Forwarding) Designated port: the port which is sending the best PBDU for 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 19 802.1w port roles Port roles RP = Root port = Designated Port AP = Alternate Port BP = Backup Port RP Hub A RP AP AP BP B HUB page 20
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 21 802.1s Before (802.1D or 802.1w) Before (with PVST) Root of 3 VLANs 1 VLANs 2 VLANs 3 VLANs 1 VLANs 2 VLANs 3 VLANs 1 VLANs 2 VLANs 3 VLANs 1 VLANs 2 VLANs 3 Root VLANs 1 VLANs 2 VLANs 3 Root of 1 Now with 802.1s VLANs 1 Root of 2 VLANs 2 VLANs 3 VLANs 1,2 VLAN 3,4 VLANs 1,2 VLAN 3,4 MSTI-1 Root VLANs 1,2 VLAN 3,4 MSTI-2 Root page 22 11
802.1s Terms MST Region: a group of switches running 802.1s under commen set of configuration attributes MST instance: an entity which will calculate his own topology. Each instance can be used for one or more VLANs Common Spanning Tree (CST): An STP or RSTP spanning tree instance to interconnect differrent regions Internal Spanning Tree (IST): RSTP instance interconnecting CST to the region. All ohter VLANs that are not configured manualy to an instance are mapped automatically to the IST = MST Instance 0. page 23 802.1s Terms CST MST Region IST page 24 12
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 25 Summary and Guide-line page 26 13
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 27 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 aware that 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 revert the cost on ProCurve to the legacy settings. page 28 14
Cisco MSTP IEEE 802.1s Standard Compliance Device Required IOS Cisco Catalyst 2950, 3550, IOS 12.2(25)SEC 3560, 3750 Cisco Catalyst IOS 12.2(25)SG 4000 No CatOS version Cisco Catalyst IOS 12.2(18)SXF 6000 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 29 Example Configuring MSTP on ProCurve/Cisco Sample topology Parameters for the MSTP are as follows: Config Name: hp-cisco Config Revision #: 1 Instance 1 VLAN 1,,20 Instance 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 page 30 15
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-1 Spanning-Tree mode mst Spanning-Tree extend system-id! Spanning-Tree mst configuration name hp-cisco revision 1 instance 1 vlan 1,, 20 instance 2 vlan 30, 40 Spanning-Tree mst 0-1 priority 0 Spanning-Tree mst 2 priority 4096 end The Cisco Switch 2 is defined as Root for instances 2 and secondary Root for instance 0 and 1. Conf t hostname Cisco-2 Spanning-Tree mode mst Spanning-Tree extend system-id! Spanning-Tree mst configuration name hp-cisco revision 1 instance 1 vlan 1,, 20 instance 2 vlan 30, 40! Spanning-Tree mst 0-1 priority 4096 Spanning-Tree mst 2 priority 0 page 31 Configuring MSTP on ProCurve ProCurve-Edge-1 and 2 are defined as edge switches. hostname "ProCurve-Edge-1/2" Spanning-Tree Spanning-Tree protocol-version MSTP Spanning-Tree config-name "hp-cisco" Spanning-Tree config-revision 1 Spanning-Tree instance 1 vlan 1 20 Spanning-Tree instance 2 vlan 30 40 Result Cisco-1#sh span mst configuration Name [hp-cisco] Revision 1 Instance Vlans mapped -------- -------------------------------------------- ----------------- 0 2-9,11-19,21-29,31-39,41-4094 1 1,,20 2 30,40 ------------------------------------------------------ ----------------- page 32 16
Useful Cisco Troubleshooting Commands CatOS sh spant summary (summary of features / ports) sh spant <vlan> active (STP state for a vlan) sh spant mst [inst] (STP state for MST instance) sh spant <mod/port> (STP state for port) sh spant stat <mod/port> <vlan> IOS sh spann summary sh spann vlan <vlan> detail sh spann mst [inst] sh spann int <int> detail sh span int <int> detail page 33 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 page 34 17
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