8600
RSTP/MSTP Technical Configuration
Guide
Avaya Data Solutions
Document Date: July 2010
Document Number: NN48500-583
Document Version: 2.1
Ethernet Routing Switch
8600, 8300, 5x00, 4500, 2500
Engineering
2
avaya.com
© 2010 Avaya Inc.
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RSTP/MSTP Technical Configuration Guide
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No
Date
Version
Revised by
Remarks
1
06/02/2009
2.0
ESE
Modifications to Software Baseline section
Abstract
This document provides an overview of Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning
Tree Protocol (MSTP).
Revision Control
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Table of Contents
Figures ......................................................................................................................................................... 5
Document Updates ..................................................................................................................................... 6
Conventions ................................................................................................................................................ 6
1. Overview: RSTP/MSTP ....................................................................................................................... 7
1.1 Interoperability with Legacy STP................................................................................................... 8
1.2 Differences in Port Roles .............................................................................................................. 9
1.3 Edge Port ...................................................................................................................................... 9
1.4 Path Cost Values ........................................................................................................................ 10
1.5 Root Bridge ................................................................................................................................. 10
1.6 Port Roles .................................................................................................................................... 10
1.7 Rapid Convergence .................................................................................................................... 12
1.8 Negotiation Process .................................................................................................................... 12
1.9 MSTP MST Region Configuration ............................................................................................... 13
1.10 Spanning Tree interoperability between Avaya and Cisco ......................................................... 14
1.11 RSTP/MSTP Definitions .............................................................................................................. 15
2. RSTP Configuration Example .......................................................................................................... 17
2.1 Configuration ............................................................................................................................... 18
2.2 Verify Operations ........................................................................................................................ 21
3. MSTP Configuration Example – One Region ................................................................................. 26
3.1 Configuration ............................................................................................................................... 28
3.2 Verify Operations ........................................................................................................................ 34
4. MSTP Configuration Example - Two Regions ................................................................................ 46
4.1 Configuration ............................................................................................................................... 48
4.2 Verify Operations ........................................................................................................................ 48
5. Software Baseline ............................................................................................................................. 60
6. Reference Documentation ................................................................................................................ 61
7. Customer service .............................................................................................................................. 62
7.1 Getting technical documentation ................................................................................................. 62
7.2 Getting product training ............................................................................................................... 62
7.3 Getting help from a distributor or reseller .................................................................................... 62
7.4 Getting technical support from the Avaya Web site .................................................................... 62
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Figures
Figure 1 Negotiation Process ...................................................................................................................... 13
Figure 2: Cisco R-PVST Interoperability with Avaya .................................................................................. 15
Figure 3: RSTP Configuration Example ...................................................................................................... 17
Figure 4: RSTP Example – Normal Data Flow ........................................................................................... 17
Figure 5: MSTP Example with One Region ................................................................................................ 26
Figure 6: MSTP Example with One Region – CIST Instance 0 Data Flow ................................................. 27
Figure 7: MSTP Example with One Region – MSTI 1 Data Flow ............................................................... 27
Figure 8: MSTP Example with One Region – MSTI 2 Data Flow ............................................................... 28
Figure 9: MSTP Example with Two Regions .............................................................................................. 46
Figure 10: MSTP Example with Two Regions – MSTI 1 Data Flow ........................................................... 47
Figure 11: MSTP Example with Two Regions – MSTI 2 Data Flow ........................................................... 47
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Tip – Highlights a configuration or technical tip.
Note – Highlights important information to the reader.
Warning – Highlights important information about an action that may result in equipment
damage, configuration or data loss.
Bold text indicates emphasis.
Italic text in a Courier New font indicates text the user must enter or select in a menu item, button
or command:
ERS5520-48T# show running-config
Output examples from Avaya devices are displayed in a Lucinda Console font:
ERS5520-48T# show running-config
! Embedded ASCII Configuration Generator Script
! Model = Ethernet Routing Switch 5520-24T-PWR
! Software version = v5.0.0.011
enable
configure terminal
Document Updates
July 2010
Conventions
This section describes the text, image, and command conventions used in this document.
Symbols:
Text:
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1. Overview: RSTP/MSTP
The original IEEE 802.1D Spanning Tree Protocol (hereby referred to as STP) standard (802.1D-1998
clause 8) provides loop protection and recovery, but, it is slow to respond to a topology change in the
network (for example, a dysfunctional link in a network).
The Rapid Spanning Tree protocol (RSTP or IEEE 802.1w / 802.1D-2004 clause 17) reduces the
recovery time after a network break down. It also maintains a backward compatibility with the original
IEEE 802.1D STP standard which was the Spanning Tree implementation prior to RSTP. Typically, the
recovery time of RSTP is within a second compared to STP which can take upwards of 30-50 seconds to
recover.
RSTP also reduces the amount of flooding in the network by enhancing the way the Topology Change
Notification (TCN) packet is generated.
The Multiple Spanning Tree Protocol (MSTP or IEEE 802.1s / 802.1Q-2005 clause 13) is an extension to
RSTP allowing for multiple Spanning Tree instances on the same switch. Both 802.1D and 802.1w
spanning tree protocols operate without any regards to a network’s VLAN configuration whereas 802.1s
maps VLANs to multiple spanning tree instances. This allows the switch to use different paths in the
network to effectively load balance or distribute VLANs evenly where each Spanning Tree instance will
block the appropriate port(s) within its own instance.
When configuring MSTP, one or more VLANs are assigned to an MST instance (MSTI) and each switch
is assigned to an MSTP MST region. Hence, each MST region consists of one or more MSTP switches
where each switch must be configured with the same VLANs, at least one MST instance, and the same
MST region name. A Common Spanning Tree (CST), base instance 0, is used to interconnect individual
MST regions or MST regions with RSTP or STP LANs. MSTP connects all switches and LANs together
with a single common and internal spanning tree (CIST) where one single CIST root bridge is elected and
one CIST regional root bridge is elected per MST region. In summary, MSTI instances provide loop free
switching within a region for VLANs whereas CIST provides loop free switching between regions with no
regards to VLANs.
As noted above, MSTP is backwards compatible with both RSTP and STP likewise RSTP with STP.
MSTP effectively uses the RSTP BPDUs extended to include region information and MSTI instance
messages. These constitute the MSTP BPDU which, like both RSTP and STP BPDUs, are always
untagged.
If an MSTP bridge detects that a neighboring bridge is operating in RSTP mode, the interconnecting
interface on the MSTP bridge will downgrade to RSTP operation, whereby only RSTP BPDUs are
generated on that interface. Likewise if an RSTP or MSTP bridge detects that a neighboring bridge is
operating in STP mode, the interconnecting interface on the MSTP/RSTP bridge will downgrade to STP
operation, whereby only STP BPDUs are generated on that interface. If a number of MSTP bridges
forming an MST Region are interconnected to RSTP/STP switches, the RSTP/STP domain will see the
MSTP region as one hop.
RSTP and MSTP achieve rapid convergence by enhancing the Port Role Transition state machine with
regards to Forwarding transitions. Whenever a failure in the network occurs and a link or node in the
active topology is broken/lost, one or more Forward transitions on some other links, previously
Discarding, are required to restore connectivity. In the original STP protocol, a Forwarding transition was
only possible after expiry of the Listening and Learning timers (30 seconds in total) which would
guarantee enough delay for every bridge in the STP domain to receive and converge on the new topology
information. With RSTP/MSTP Forward transition delays can be dramatically reduced via the Proposal &
Agreement exchanges whereby every bridge wanting to perform a Forward transition on a Designated
port can propose such a change to it’s downstream peer bridge and can do so as soon as agreed by it’s
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peer (without having to wait for timers to expire). This process ripples throughout the RSTP/MSTP
instance domain, away from the root bridge, until all switches in the domain have converged on the new
topology.
This fast Forward transition mechanism allows RSTP/MSTP to reconverge in about 1 or 2 seconds,
depending on the number of bridges participating in the RSTP/MSTP instance and on the type of failure.
However, fast Forwarding transitions are only possible under certain conditions. The port which needs to
transition into Forwarding state must (a) be operating in Full Duplex mode and (b) there must be an
MSTP/RSTP bridge at the other end of that link.
Hence, in the presence of legacy half-duplex links (where a hub segment could result in more than one
bridge neighbor) RSTP/MSTP will fall back on the legacy STP timers. Also in the case of switch ports
where end stations are directly connected condition (b) is not satisfied and again legacy STP timers are
used (in this case, to obtain fast Forwarding transitions, the port needs to be configured as an Edge Port
as discussed later).
Failure of the Root bridge for the RSTP/MSTP instance, while still an improvement on STP, can also
result in higher convergence times. Typically a root bridge failure where its immediate neighbors detect a
link loss on their interfaces will result in a 2 seconds reconverge time. However if the root bridge fails and
its immediate neighbors do not detect this via loss of link (for instance, a software failure on the root
device), then the reconverge time occurs after 2 consecutive BPDUs are missed i.e. 6 seconds
Overall, RSTP and MSTP enable the switch to achieve the following:
Reduce convergence time from 30-50 seconds to less than 1 or 2 seconds under most (but not
all) failure conditions
Eliminate unnecessary flushing of the MAC database and flooding of traffic to the network, with a
new enhanced Topology Change mechanism whereby only a fraction of the MAC tables need to
be flushed and re-learnt
Backward compatibility with other switches that are running legacy 802.1D STP or Avaya MSTG
(STP group 1 only).
The user can configure an Avaya switch to run Avaya STP, RSTP (802.1w), or MSTP (802.1s)
configuration.
1.1 Interoperability with Legacy STP
RSTP provides a new parameter ForceVersion for backward compatibility with legacy STP. You can
configure a port in either STP compatible mode or RSTP mode.
An STP compatible port transmits and receives only STP BPDUs. Any RSTP BPDU that the port
receives in this mode will be discarded.
An RSTP port transmits and receives only RSTP BPDUs. If an RSTP port receives an STP BPDU
it becomes an STP port. User intervention is required to bring this port back to RSTP mode. This
process is called Port Protocol Migration.
Normally an RSTP or MSTP bridge will automatically detect the STP version type of a neighboring bridge
and automatically adapt to that STP version without having to use the ForceVersion parameter.
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Port Role
STP
RSTP
MSTP
Description
Root
Yes
Yes
Yes
On a non-root bridge, this port is receiving BPDUs
with the lowest root path cost, i.e. this port is the
best path to reach the Root bridge in the
STP/RSTP domain or in the CIST or MSTI
instance for MSTP. The Root port is always in
Forwarding state.
Designated
Yes
Yes
Yes
The bridge owning this port (Designated Bridge)
has the lowest root path cost towards the Root
bridge for this segment and, in case of a tie, best
Bridge priority and Port priority. This port will
generate BPDUs every 2 seconds on the segment
and will transition in Forwarding state.
Backup
No
Yes
Yes
A bridge port that is not Root port or Designated
port is a Backup port if the same bridge is already
the Designated Bridge for the same segment (via
a different port). A Backup port is always in
Discarding state.
Alternate
No
Yes
Yes
A bridge port that is not Root port or Designated
port or Backup port is an Alternate port. An
Alternate port is always in Discarding state.
Master
No
No
Yes
On an MSTP MSTI instance only, this port is on
an MST region boundary and has the lowest root
path cost towards the CIST Root bridge (CIST
Regional Root)
1.2 Differences in Port Roles
RSTP is an enhanced version of STP. These two protocols have almost the same set of parameters.
Table 1 lists the differences in port roles for STP and RSTP. STP supports 2 port roles while RSTP
supports four port roles. MSTP adds an extra role for MSTI instances only.
Table 1 Difference in Port Roles for STP and RSTP
1.3 Edge Port
Edge port is a new parameter that is supported by RSTP/MSTP. When a port is connected to a nonswitch device such as a PC or a workstation, it must be configured as an Edge port or else it will take 30
seconds to transition into a Forwarding state. An active Edge port is similar to the STP FastStart feature
in that the port can go directly into Forwarding state without any delay. An Edge port always generates
BPDUs but immediately becomes a non Edge port if it receives a BPDU.
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Link speed
Recommended value
Less than or equal 100Kb/s
1 Mb/s
10 Mb/s
100 Mb/s
200,000,000
20,000,000
2,000,000
200,000
1 Gb/s
10 Gb/s
100 Gb/s
20,000
2,000
200
1 Tb/s
10 Tb/s
20
2
1.4 Path Cost Values
RSTP and MSTP recommend new path cost values that support a wide range of link speeds. Table 2 lists
the recommended path cost values.
Table 2 Recommended Path Cost Values
1.5 Root Bridge
Just as in STP, with RSTP and MSTP instances, the root bridge is always the bridge with the lowest
Bridge ID within the Spanning Tree instance. The Bridge ID is made up by pre-pending the bridge priority
(2 bytes) with the Bridge MAC address (6 bytes) forming an 8 byte long Bridge ID. Hence if multiple
bridges are configured with the same bridge priority, the bridge MAC address will act as a tie breaker and
uniquely determine the Root bridge.
In a Spanning Tree design, always ensure that a Core node acts as the Root Bridge.
1.6 Port Roles
Root Forwarding Port
A port receiving the best BPDU on the switch is the root port and is referred to as a Root Forwarding (RF)
port. This is the port that is the closest to the root bridge in terms of path cost. The spanning tree
algorithm elects a single root bridge in a bridged network per spanning tree instance. The root bridge is
the only bridge in a network that does not have root ports; all ports on a root bridge are normally
Designated Forwarding (DF). There can only be one path towards a root bridge on a given segment
otherwise there will be loops.
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Designated Forwarding Port
All bridges connected on a given segment listen to each other’s BPDUs and agree on the bridge sending
the best BPDU as the designated bridge for the segment. The corresponding port on the bridge is
referred to as a Designated Forwarding (DF) Port.
Alternate Discarding Port
An Alternate Discarding port is defined as a port which is not the Root port, not a Designated port and not
a Backup port. An Alternate Discarding (AD) port is a port that is blocked by receiving more useful BPDUs
from another bridge.
Backup Discarding Port
A Backup Discarding (BU) port is defined as a port that is blocked by receiving more useful BPDUs from
the bridge itself on a shared segment.
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1.7 Rapid Convergence
In RSTP and MSTP, the designated port can ask its peer for permission for going to the Forwarding
State. If the peer agrees, then the designated port moves to the Forwarding State without any delay. This
procedure is called the Negotiation Process.
RSTP and MSTP also allow information received on a new Root port to be forwarded downstream
immediately if the original Root port becomes dysfunctional instead of waiting for the Maximum Age time
(20 seconds timer). Also a new Root port can transition to Forwarding immediately provided that any
previous Root ports are in a Discarding state.
The example in Figure 1 illustrates how an RSTP port state moves rapidly to Forwarding state without the
risk of creating a loop in the network.
Switch A: ports 1 and 2 are in full duplex. Port 2 is an Edge port
Switch B: ports 1, 2 and 3 are in full duplex. Port 2 is an Edge port
Switch C: ports 1 and 2 are in full duplex. Port 2 is an Edge port
Switch A is the Root
1.8 Negotiation Process
After power up, all ports assume the role as Designated ports. All ports are in the Discarding state except
Edge ports. Edge ports go directly to Forwarding state without delay.
Switch A port 1 and switch B port 1 exchange BPDUs and switch A knows that it is the Root bridge and
switch A port 1 is the Designated port for that segment. Switch B learns that switch A has the lowest cost
to reach the Root. Switch B port 1 becomes Root port and since there is no other previous Root port
active on Switch B it can transition into Forwarding state. Switch A port 1 is still in Discarding state at this
point.
Switch A starts the negotiation process by sending a BPDU with proposal bit set on its port 1 to Switch B.
Switch B receives proposal BPDU and this will force it to enter the sync process whereby all its
Designated non-Edge ports (in this case only port 3 to Switch C) are put in Discarding state and in turn a
negotiation process for them is triggered downstream
Switch B can now send a BPDU with the agreement bit set back to switch A.
Switch A can now transition port 1 into Forwarding state. PC 1 and PC 2 can talk to each other.
In the meantime the negotiation process also moved down to switch B port 3 and its partner port
on Switch C.
PC 3 cannot talk to either PC 1 or PC 2 until the negotiation process between switch B and switch
C is complete.
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Figure 1 Negotiation Process
The RSTP convergence time depends on how quickly the switch can exchange BPDUs during the
Negotiation process, and the number of switches in the network. The convergence time depends on the
hardware platform and number of active applications running on the switch.
1.9 MSTP MST Region Configuration
One of the more complex aspects of MSTP is the MST Region configuration. In order for a number of
MSTP bridges to share multiple MSTI instances (and therefore achieve some level of traffic load
balancing across VLANs belonging to different MSTI instances) they must first be all members of the
same MST Region. If that is not the case, then any MSTI instance configured will never extend beyond
the local bridge and it’s forwarding topology will simply be collapsed onto the CIST forwarding topology
(i.e. no per VLAN load balancing will ever be possible). The CIST base instance of MSTP will however
work whether or not any MST Regions exist.
To belong to the same MST Region, MSTP bridges must have an identical MST Configuration Identifier
(MCID). The MCID contains the following components:
The MCID Format Selector version: A single byte of value 0 in the current MSTP specification; on
the Avaya ERS products this value is exposed and configurable however it should be left at
default value 0.
The Region name: A variable length text string which must be manually configured to be the
same across all MSTP bridges which need to operate in the same region.
The Region Revision Level or Version: A 2 byte field which should either be left at default value 0
or configured to be the same across all MSTP bridges which need to operate in the same region.
The VLAN MSTI membership Configuration Digest: This is a hash signature of the mapping of
every possible vlan-id (1-4095) to an MSTI/CIST instance. This component is not directly user
configurable but is automatically generated by the MSTP bridge based upon what VLANs are
created and to which MSTI or CIST instance they are assigned.
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Hence, note that simply configuring the same Region Name and Region Version on all MSTP
bridges is not sufficient to make them belong to the same MST Region. It is also necessary for
them to have the same exact VLANs configured and these VLANs need to be assigned to exactly
the same CIST/MSTI instances across all MSTP bridges.
To confirm whether an MSTP bridge belongs to the desired MST Region, the MSTP standard
defines the role of the CIST Regional root which identifies the bridge within the MST Region with
the lowest external Root path cost, on a Region boundary port, towards the CIST Root. If the
CIST Root exists within the MST Region, then the CIST Regional root is the CIST Root bridge.
Once a number of MSTP bridges agree on a same CIST Regional root, they are actively part of
the same MSTP Region and can now share MSTI instances.
1.10 Spanning Tree interoperability between Avaya and
Cisco
Cisco supports three Spanning Tree modes of operation, PVST+, Rapid-PVST, and MST. Of the three,
only MST support standards based 802.1s which can interoperate with any of Avaya switches offered
today. In regards to the ERS8600 only, it also supports the older PVST+ Spanning Tree mode of
operation.
By default, Cisco comes enabled with Rapid-PVST. This proprietary protocol combines the functionality of
RSTP with PVST creating an RSTP (802.1w) instance per VLAN. The Cisco implementation also defines
a concept of ―native‖ VLAN whereby BPDUs generated for the native vlan are standard compliant
(802.1w for Rapid-PVST) whereas BPDUs generated for all other VLANs are modified with a Cisco
multicast MAC address and are q-tagged with the vlan-id they belong to, thus rendering them
incompatible with the standard.
It is therefore highly recommended to avoid Cisco’s proprietary Rapid-PVST and enable instead MST on
Cisco and MSTP on the Avaya switches.
It is still possible to make the Rapid-PVST protocol interoperate with Avaya standards based 802.1w
(RSTP) by letting Cisco’s native VLAN instance interoperate with Avaya single RSTP instance and
allowing the other Cisco Spanning Tree instances to be flooded transparently across the Avaya switches.
The native VLAN by default is set to VLAN 1. This method will work providing the native RSTP instance
on an Avaya switch never blocks any interface. Hence, it can get a little difficult setting up a network.
If the Avaya switches are being deployed as edge switches onto a Cisco Core using Rapid-PVST an even
better approach is to simply disable Spanning Tree on the Avaya switch uplink ports to the Cisco core
and let the Cisco core take care of any loops. This is illustrated in Figure 2. The proprietary BPDUs
generated by the Cisco Core will simply be re-flooded in the vlan by the Avaya edge switch and thus one
of the Cisco’s will block one of the uplinks. Note that in this design only non-native VLANs must be tagged
on the uplinks to the Avaya switches. The native VLAN on the Cisco Core needs to be set to some
unused vlan; for instance left configured at default VLAN 1 which should never be used.
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Figure 2: Cisco R-PVST Interoperability with Avaya
1.11 RSTP/MSTP Definitions
As per the IEEE 802.1s (MSTP) [integrated in IEEE 802.1Q-2005] and IEEE 802.1w (RSTP) [integrated
in IEEE 802.1D-2004] standards:
Boundary Port: A Bridge Port attaching an MST Bridge to a LAN that is not in the same region.
Common and Internal Spanning Tree (CIST): The single Spanning Tree calculated by STP and RSTP
together with the logical continuation of that connectivity through MST Bridges and regions, calculated by
MSTP to ensure that all LANs in the Bridged Local Area Network are simply and fully connected.
Common Spanning Tree (CST): The single Spanning Tree calculated by STP and RSTP, and by MSTP
to connect MST Regions.
Internal Spanning Tree (IST): An internal Spanning Tree that runs in a given MST Region. Within a MST
region, multiple Spanning Instances may be configured. Instance 0 within a region is known as the
Internal Spanning Tree (IST).
Multiple Spanning Tree (MST) Configuration Identifier: A name for revision level, and a summary of a
given allocation of VLANs to Spanning Trees.
NOTE - Each MST Bridge uses a single MST Configuration Table and Configuration Identifier.
MST Configuration Table: A configurable table that allocates each and every possible VLAN to the
Common Spanning Tree or a specific Multiple Spanning Tree Instance.
Multiple Spanning Tree Algorithm and Protocol (MSTP): The Multiple Spanning Tree Algorithm and
Protocol.
MST Bridge: A Bridge capable of supporting the CST, and one or more MSTIs and of selectively
mapping frames classified in any given VLAN to the CST or a given MSTI.
MST Region: A set of LANs and MST Bridges physically connected via Ports on those MST Bridges,
where each LAN’s CIST Designated Bridge is an MST Bridge, and each Port is either the Designated
Port on one of the LANs, or else a non-Designated Port of an MST Bridge that is connected to one of the
LANs, whose MST Configuration Identifier (MCID) matches exactly the MCID of the Designated Bridge of
that LAN.
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NOTE - It follows from this definition that the MCID is the same for all LANs and Ports in the Region and
that the set of MST Bridges in the region are interconnected by the LANs.
Multiple Spanning Tree Bridge Protocol Data Unit (MST BPDU): The MST BPDU specified.
Multiple Spanning Tree Instance (MSTI): One of a number of Spanning Trees calculated by MSTP
within an MST Region, to provide a simply and fully connected active topology for frames classified as
belonging to a VLAN that is mapped to the MSTI by the MST Configuration Table used by the MST
Bridges of that MST Region.
Rapid Spanning Tree Algorithm and Protocol (RSTP): The Rapid Spanning Tree Algorithm and
Protocol.
Rapid Spanning Tree Bridge Protocol Data Unit (RST BPDU): The RST BPDU specified.
Single Spanning Tree (SST) Bridge: A Bridge capable of supporting only a single spanning tree, the
CST. The single spanning tree may be supported by the Spanning Tree Algorithm and Protocol (STP)
defined in IEEE Std 802.1D, 1998 Edition, or by the Rapid Spanning Tree Algorithm and Protocol (RSTP),
defined in IEEE Std 802.1w-2001.
Spanning Tree: A simple, fully connected active topology formed from the arbitrary physical topology of
connected Bridged Local Area Network components by relaying frames through selected bridge ports and
not through others. The protocol parameters and states used and exchanged to facilitate the calculation
of that active topology and to control the bridge relay function.
Spanning Tree Algorithm and Protocol (STP): The Spanning Tree Algorithm and Protocol described in
Clause 8 of IEEE Std 802.1D, 1998 Edition.
Spanning Tree Bridge Protocol Data Unit (ST BPDU): A Bridge Protocol Data Unit specified for use by
the Spanning Tree Algorithm and Protocol, i.e. a Configuration or Topology Change Notification BPDU as
described in Clause 9 of IEEE Std 802.1D, 1998 Edition.
Abbreviations
CIST Common and Internal Spanning Tree
CST Common Spanning Tree
IST Internal Spanning Tree
MCID MST Configuration Identifier
MST Multiple Spanning Tree
MST BPDU Multiple Spanning Tree Bridge Protocol Data Unit
MSTI Multiple Spanning Tree Instance
MSTP Multiple Spanning Tree Protocol
RST BPDU Rapid Spanning Tree Bridge Protocol Data Unit
RSTP Rapid Spanning Tree Protocol
SST Single Spanning Tree
ST BPDU Spanning Tree Bridge Protocol Data Unit
STP Spanning Tree Protocol
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2. RSTP Configuration Example
Figure 3: RSTP Configuration Example
In this configuration example, we will accomplish the following:
Configure the bridge priority as shown in Figure 3. This will result in 8600-1 becoming the RSTP
Root Bridge. If 8600-1 should fail, then 8600-2 should become the Root Bridge based on priority
settings.
Two VLANs will be configured, a management VLAN (VLAN 200) and a end user VLAN (VLAN
1000)
For the management VLAN 200, we will configure a management IP address as shown in the
diagram above – for this example, no routes are configured for the management as it is a simple
Layer 2 network
As an option, we can set the RSTP port priority on 8600-1 to influence the link taken between
8600-1 and 8600-2. The default port priority simply has to be changed to a lower value on 8600-1
from the default setting of 128
The port priority setting is configured in increments of 16 from 0 to 240
After all the switches have been configured using the above settings, traffic should flow as that shown in
the following diagram.
Figure 4: RSTP Example – Normal Data Flow
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ERS8600-1: Step 1 – Set the bootconfig Spanning Tree mode to RSTP
ERS-8610:5(config)# boot config flags spanning-tree-mode rstp
ERS-8610:5(config)# save bootconfig
ERS-8610:5(config)# boot –y
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ERS-8610:5(config)#sys name ERS8600-1
ERS8600-2: Step 1 – Set the bootconfig Spanning Tree mode to RSTP
ERS-8610:5# config bootconfig flags spanning-tree-mode rstp
ERS-8610:5# save bootconfig
ERS-8610:5# boot –y
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ERS-8610:5# config sys set name ERS8600-2
ERS4550T-1: Step 1 – Set Spanning Tree Operation mode to RSTP
4550T(config)# spanning-tree op-mode rstp
4550T(config)# write memory
4550T(config)# boot
Reboot the unit(s) (y/n) ? y
|
4550T(config)# snmp-server name 4550T-1
4550T-1(config)# banner disabled
ERS4528GT-2: Step 1 – Set Spanning Tree Operation mode to RSTP
4548GT#(config)# spanning-tree op-mode rstp
4548GT#(config)# write memory
4548GT#(config)# boot
Reboot the unit(s) (y/n) ? y
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4548GT(config)# snmp-server name 4548GT-2
4548GT(config)# banner disabled
2.1 Configuration
For this configuration example, 8600-1 will be configured using ACLI while 8600-2 will be configured
using PPCLI.
2.1.1 Set Spanning Tree Mode to RSTP
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ERS8600-1: Step 1 – Create VLANs 200 and 1000 and add port members
ERS8600-1:5(config)# vlan create 200 name mgmt type port-mstprstp 0
ERS8600-1:5(config)# vlan create 1000 type port-mstprstp 0
ERS8600-1:5(config)# vlan ports 4/23,4/24,1/33,1/35 tagging tagAll
ERS8600-1:5(config)# vlan members remove 1 1/5,4/23,4/24,1/33,1/35
ERS8600-1:5(config)# vlan members add 200 4/23,4/24,1/33,1/35
ERS8600-1:5(config)# vlan members add 1000 1/5,4/23,4/24,1/33,1/35
ERS8600-2: Step 1 – Create VLANs 200 and 1000 and add port members
ERS8600-2:5# config vlan 200 create byport-mstprstp 0 name mgmt
ERS8600-2:5# config vlan 1000 create byport-mstprstp 0
ERS8600-2:5# config ethernet 1/23,1/24,1/34,1/36 perform-tagging enable
ERS8600-2:5# config vlan 1 ports remove 1/5,1/23,1/24,1/34,1/36
ERS8600-2:5# config vlan 200 ports add 1/23,1/24,1/34,1/36
ERS8600-2:5# config vlan 1000 ports add 1/5,1/23,1/24,1/34,1/36
ERS4550T-1: Step 1 – Create VLANs 200 and 1000 and add port members
4550T-1(config)# vlan create 200 name mgmt type port
4550T-1(config)# vlan create 1000 type port
4550T-1(config)# vlan configcontrol automatic
4550T-1(config)# vlan ports 33,34 tagging tagall
4550T-1(config)# vlan members add 200 33,34
4550T-1(config)# vlan members add 1000 5,33,34
4550T-1(config)# vlan members remove 1 5,33,34
ERS4528GT-2: Step 1 – Create VLANs 200 and 1000 and add port members
4548GT-2(config)# vlan create 200 name mgmt type port
4548GT-2(config)# vlan create 1000 type port
4548GT-2(config)# vlan configcontrol automatic
4548GT-2(config)# vlan ports 35,36 tagging tagall
4548GT-2(config)# vlan members add 200 35,36
4548GT-2(config)# vlan members add 1000 5,35,36
4548GT-2(config)# vlan members remove 1 5,35,36
ERS8600-1: Step 2 – Add management IP address and add port members
ERS8600-1:5(config)# interface vlan 200
RSTP/MSTP Technical Configuration Guide
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