cis187-4-PVST-RSTP

Enhancements to 802.1D, PVST+, RSTP and MST

CIS 187 Multilayer Switched Networks

CCNP SWITCH

Rick Graziani

Spring 2010

Rick Graziani [email protected] 2

Additional Notes

• See Notes section for additional detailed information.


Download this file

• Download: PT-Topology-STP2.pkt


Cisco’s RSTP is Rapid PVST+


IEEE Documents

• IEEE 802.1D - Media Access Control (MAC) bridges

• IEEE 802.1Q - Virtual Bridged Local Area Networks

• IEEE 802.1w - Rapid Reconfiguration (Supp. To 802.1D)

• IEEE 802.1s - Multiple Spanning Tree (Supp. To 802.1Q)


Enhancements to STP

• STP – PortFast– BPDU Guard– Root Guard– UplinkFast– BackboneFast

• Per VLAN Spanning Tree (PVST+)

• Rapid Spanning Tree Protocol (RSTP)

• Multiple Spanning Tree Protocol (MST)– MST is also known as Multiple Instance Spanning Tree

Protocol (MISTP) on Cisco Catalyst 6500 switches and above

Helping STP protect your LAN from Problems

PortFast

BPDU Guard

Root Guard

UplinkFast

BackboneFast


Powercycle a host and watch link lights…

How long until switch link light turns green?


PortFast

• Host powered on.

• Port moves from blocking state immediately to listening state (15 seconds).– Determines where switch fits into spanning tree topology.

• After 15 seconds port moves to learning state (15 seconds). – Switch learns MAC addresses on this port.

• After 15 seconds port moves to forwarding state (30 seconds total).

Powered On

Blocking StateListening StateLearning StateForwarding State I’m adding any addresses on this port to my MAC Address

Table.


PortFast – Problem DHCP

• Host sends DHCP Discovery• Host never gets IP addressing information

• Also: Insignificant Topology Change – A users PC causes the link to go up or down (normal booting or shutdown process).– No significant impact but given enough hosts switches could be in a constant state

of flushing MAC address tables.– Causes unknown unicast floods.

Powered On

Blocking StateListening StateLearning StateForwarding State

DHCP DiscoveryTimeout

IP Address = 169.x.x.x


PortFast

• The purpose of PortFast is to minimize the time that access ports wait for STP to converge.

• When a port comes up, the port immediately moves into Forwarding state.

• The advantage of enabling PortFast is to prevent DHCP timeouts.

• Host sends DHCP Discovery

• Host can now can IP addressing information.

Powered On

Portfast enabledForwarding State

DHCP Discovery

DHCP Offer


Configuring Portfast

Access2(config)#interface range fa 0/10 - 24Access2(config-if-range)#switchport mode access

<Previously configured>Access2(config-if-range)#spanning-tree portfast

• Warning: PortFast should only be enabled on ports that are connected to a single host.

• If hubs or switches are connected to the interface when PortFast is enabled, temporary bridging loops can occur.

• If a loop is detected on the port, it will move into Blocking state.

ORAccess2(config)#spanning-tree portfast default


Powercycle the host again (portfast enabled)

How long until switch link light turns green?


Configuring Portfast

Switch(config)#interface range fa 0/10 - 24Switch(config-if-range)#switchport mode access

<Previously configured>Switch(config-if-range)#spanning-tree portfast

Configure Portfast on all Distribution and Access switches


Verifying Portfast

Switch(config)# show spanning-tree inteface type mod/num portfast


• Uplinkfast allows access layer switches that have redundant links to multiple distribution switches the ability to converge quickly when a link has failed.

– For “Leafs” (end nodes) of the spanning tree.

– Not for use within backbone or distribution switches (BackboneFast).

UplinkFast


• UplinkFast must have direct knowledge of the link failure in order to move a blocked port into a forwarding state.

• Single Root Port but multiple potential root ports.• If Root Port fails, next-lowest path cost is unblocked and used without delay

(almost).– This switchover occurs within 1 second.

Root

X

Unblock G 1/1 skips listening and learning and goes directly to forwarding

UplinkFast


• Uplinkfast is enabled for the entire switch and all VLANs.

– Not supported on a per-VLAN basis.

• Uplinkfast keeps track of all possible paths to the Root Bridge.

– So, not allowed on the Root Bridge

– Switches BID: Raised to 49,152 to make it unlikely it will be the Root Bridge.

Access1(config)#spanning-tree uplinkfast

UplinkFast

Not supported with Packet Tracer


• Backbone fast is a Cisco proprietary feature that, once enabled on all switches can save a switch up to 20 seconds (Max Age) when it recovers from an indirect link failure.

• Configured in global configuration mode and should be enabled on all switches in the network.

– Requires the use of RLQ (Root Link Query) requests and replies.– Disabled by default.

BackboneFast Root

X

Switch(config)#spanning-tree backbonefast


• BackboneFast is initiated when a root port or blocked port on a switch receives inferior BPDUs from a designated bridge.

• Inferior BPDUs are sent from a designated bridge that has lost its connection to the root bridge.

• Normally, a switch must wait for Max Age (20 seconds) to expire before responding to an inferior BPDU.

• With Backbonefast, switch determines alternate paths to Root.

RP X

Inferior BPDU

BlockingForwarding

My link to the Root has gone down. I have no alternate

path to it. So, I’m the new

root and send out my BPDUs

on all ports.

This new BPDU is inferior to the

one it had stored for this port so I

will ignore it. Let me send my current Root a query (RLQ).

I just heard from Core that they are still the Root. I will:• Send BPDU to D1• Transition port immediately to listening state saving 20 seconds (Max Age)

Thanks for telling me Core is the Root. I

will change my RP to Fa 0/5.

RP After 20 seconds this port will now go into Forwarding state.

Listening

Root


FYI – More Information• An inferior BPDU identifies one switch as

both the root bridge and the designate bridge.

• Distribution 1 is the Designated Bridge.• Normally, sends BPDUs with Root Bridge

as the Core BID.• Inferior BPDU – A received BPDU that

identifies the root bridge and the designated bridge as the same switch. (“I was only just the Designated Bridge, but now that I can’t get to the Root Bridge, so now I am also the Root Bridge.”)

BackboneFast

= Core

= Dist1

= Dist1

= Dist1Same Switch

Normal BPDU

Inferior BPDU


Protecting against unexpected BPDUs

• Root Guard

• BPDU Guard

• Loop Guard

• Coast Guard


• A port configured with PortFast will go into blocking state if it receives a Bridge Protocol Data Unit (BPDU).

• This could lead to false STP information that enters the switched network and causes unexpected STP behavior.

• Newly connected switch could advertise itself as the root.• BPDU Guard: Developed to protect integrity of switch ports with

PortFast enabled but also keeps maintains STP integrity by disallowing unauthorized switches.

Portfast

X

Blocking and now listening to BPDUs

Forwards BPDUs to other switches.

STP Reconvergence?

BPDU

Problem: Unexpected BPDUs


• When the BPDU guard feature is enabled on the switch, STP shuts down PortFast enabled interfaces that receive BPDUs instead of putting them into a blocking state.

– Errdisable: Port must be manually re-enabled or automatically recovered via timers.• BPDU guard will also keep switches added outside the wiring closet by users from

impacting and possibly violating Spanning Tree Protocol.

Distribution1(config)#interface range fa 0/10 - 24Distribution1(config-if-range)#spanning-tree bpduguard enable

BPDU

|

Err-Disable, Shutdown

Portfast & BPDU Guard

No BPDUs sent

Solution: BPDU Guard

Not supported with Packet Tracer


• Root Guard prevents a switch from becoming the root bridge.– Typically access switches

• Configured on switches that connect to this switch.

Potential Root

Protect Protect

Potential Root

Root Guard


Root Guard

Distribution1(config)#interface fa 0/3Distribution1(config-if-range)#spanning-tree guard rootDistribution1(config)#interface gig 0/2Distribution1(config-if-range)#spanning-tree guard rootDistribution2(config)#interface fa 0/3Distribution2(config-if-range)#spanning-tree guard rootDistribution2(config)#interface gig 0/1Distribution2(config-if-range)#spanning-tree guard root

Access2(config)#no spanning-tree uplinkfast

• UplinkFast must be disabled because it cannot be used with root guard.


• This message appears after root guard blocks a port:

%SPANTREE-2-ROOTGUARDBLOCK: Port 0/3 tried to become non-designated in VLAN 1. Moved to root-inconsistent state

Root Guard

Root Guard

Superior BPDU

I want to be root bridge!

STP Inconsistent State – no traffic is passed.

I no longer want to be root. I have

been reconfigured to be a non-root bridge.

I will now transition to listening sate, then learning state, then forwarding sate.


Unidirectional Link Detection Protocol (ULDP)

• Spanning-Tree Protocol (STP) resolves redundant physical topology into a loop-free, tree-like forwarding topology.

• This is done by blocking one or more ports.

Blocked Port

Designated Port


ULDP

• STP uses Bridge Protocol Data Units (BPDUs). • If a switch’s port in blocking port stops receiving BPDUs:

– STP eventually ages out the STP information for the port (up to 50 secs) – Moves port to forwarding state.

• This creates a forwarding loop or STP loop. • How is it possible for the switch to stop receiving BPDUs while the port is up?

– The reason is unidirectional link.

BPDU

No BPDU’s Received

Change to Forwarding State

Loop!

BPDU

BPDU

BPDU

BPDU

BPDU


ULDP

• RFC 5171: “Issues arise when, due to mis-wirings or to hardware faults, the communication path behaves abnormally and generates forwarding anomalies.

• Link fails in the direction of SwitchC. – SwitchC stops receiving traffic from SwitchB.– However, SwitchB still receives traffic from C.

• UDLD is a Layer 2 (L2) protocol that works with the Layer 1 (L1) mechanisms to determine the physical status of a link.

No BPDU’s ReceivedChange to Forwarding State

BPDU


ULDP

• Enable both auto-negotiation and UDLD to prevent unidirectional connection.

• With UDLD switches share Device/Port ID information.

Layer 1: Auto-negotiation configured (speed/duplex)

Layer 2: UDLD configured

My device/port ID & your device port ID



ULDP

• Port shutdown by UDLD remains disabled until:– Manually reenabled or – errdisable timeout expires (if configured)


My device/port ID & your device port IDX Unidirectional link failure

UDLD-3-DISABLE: Unidirectional link detected on port 1/2. Port disabled

Port disabled


Configuring ULDL

Switch(config)# udld {enable | aggressive}

or

Switch(config)# interface fa 1/2

Switch(config-if)# udld {enable | aggressive}

• Normal mode (enable) – Port is allowed to continue it’s operation merely marks the port as being in undetermined state and generates a syslog message.

• Aggressive mode – Port is place in Errdisable state and cannot be used.


Loopguard

• Loopguard also protects against ports erroneously transitioning to forwarding mode.

• Loopguard will also protect against STP failures, designated switch not sending BPDUs due to software problems.

No BPDU’s Received

Change to Forwarding State

BPDUXLoop!

No Loopguard Configured


Loopguard

• If the switch begins to receive BPDUs again, it will transition through normal STP states.

• Loopguard does NOT protect against problems due to wiring issues.

• Highest level of protection is to enable both Loopguard and UDLD.

BPDU

BPDU X Unidirectional link failure

%SPANTREE-2-LOOPGUARD_BLOCK: Loop guard blocking port FastEthernet1/0 on VLAN0010

Inconsistent Blocking StateLoopguard Configured


Configuring Loopguard

Switch(config)# spanning-tree loopguard default

or

Switch(config)# interface fa 1/2

Switch(config-if)# spanning-tree guard loop

RSTP – IEEE 802.1w (Rapid Spanning Tree Protocol)




Rapid Spanning Tree Protocol


Rapid Spanning Tree Protocol

• The immediate hindrance of STP is convergence. • Depending on the type of failure, it takes anywhere from 30 to 50

seconds, to converge the network. • RSTP helps with convergence issues that plague legacy STP.


STP vs RSTP

• RSTP is based on IEEE 802.1w standard.• IEEE 802.1w took 802.1D’s principle concepts and made convergence

faster.• STP topology change takes 30 seconds (two intervals of Forward Delay timer).• RSTP is proactive and therefore negates the need for the 802.1D delay timers. • RSTP (802.1w) supersedes 802.1D, while still remaining backward compatible.• RSTP BPDU format is the same as the IEEE 802.1D BPDU format, except that

the Version field is set to 2 to indicate RSTP.• The RSTP spanning tree algorithm (STA) elects a root bridge in exactly the

same way as 802.1D elects a root.

vs

802.1D 802.1w


RSTP

• RSTP can be applied on Cisco switches as:– A single instance per VLAN

• Rapid PVST+ (RPVST+)– Multiple instances

• IEEE 802.1s Multiple Spanning Tree (MST)


STP Port Behavior and States

• 802.1D– Ports

• Root Port• Designated Port• Blocking Port

– Not Designated Port and Not Root Port– Cisco’s proprietary UplinkFast has a hidden Alternative Port

offering parallel paths, but in Blocking state.– States

• Disabled (Not 802.1D state)• Blocking• Listening• Learning• Forwarding

– Only state that sends/receives data.


RSTP

Root Bridge: Same election process as 802.1D (lowest BID)Ports• Root Port (802.1D Root Port)

– The one switch port on each switch that has the best root path cost to the root.

• Designated Port (802.1D Designated Port)– The switch port on a network segment that has the

best root path cost to the root.• Alternate Port (802.1D Blocking Port)

– A port with an alternate path the root.– An alternate port receives more useful BPDUs from

another switch and is a port blocked.– Similar to how Cisco UplinkFast works.

• Backup Port (802.1D Blocking Port)– A port that provides a redundant (but less desirable)

connection to a segment where another switch port already connects.

– A backup port receives more useful BPDUs from the same switch it is on and is a port blocked.


RSTP Port States

Operational Port State

STP Port State RSTP Port State

Disabled Disabled Discarding

Enabled Blocking Discarding

Enabled Listening Discarding

Enabled Learning Learning

Enabled Forwarding Forwarding

• RSTP defines port states based on what it does with incoming data frames.• Discarding

– Incoming frames are dropped– No MAC Addresses learned – Combination of 802.1D (Disabled), Blocking and Listening

• Learning– Incoming frames are dropped– MAC Addresses learned

• Forwarding– Incoming frames are forward.


RSTP BPDUs

• RSTP uses same 802.1D BPDU format for backward compatibility.– 802.1D and 802.1w switches can coexist.

• BPDUs sent out every switch port at Hello Time intervals regardless if BPDUs are sent on the port.

• When three BPDUs in a row (6 seconds) are missed:– the neighbor switch is presumed down– All MAC address information pointing to that switch (out that port) is

immediately aged out (flushed)– Switch can detect a neighbor down in 6 seconds instead of MaxAge

of 20 seconds.

STP Port State STP BPDUs RSTP Port State RSTP BPDUs

Disabled Not Sent/Received Discarding Not Sent/Received

Blocking Receive only Discarding Sent/Received

Listening Sent/Received Discarding Sent/Received

Learning Sent/Received Learning Sent/Received

Forwarding Sent/Received Forwarding Sent/Received


RSTP Convergence

• http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swmstp.html#wp1048403

• Convergence is a two step process:

1. Elect a Root Bridge

2. Examine all switch ports which by default are in Blocking state and advance to the appropriate state to prevent loops.

• STP requires the expiration of several timers before switch ports can be moved to Forwarding state.

• RSTP takes a different approach:

– When a switch joins the topology (powered-up) or detects a failure in the existing topology…

– Determines its forwarding decisions based on the type of port.

• Edge Port

• Root Port

• Point-to-Point Port

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swmstp.html#wp1048403

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swmstp.html#wp1048403


Edge Ports

• Edge port will never have a switch connected to it so cannot form bridging loops.

• Immediately transitions to forwarding state.

• Traditional identified with STP PortFast feature.

• For familiarity the command is the same: spanning-tree portfast

• Never generates topology changes notifications (TCNs) when the port transitions to a disabled or enabled status.

• If an edge port receives a BPDU, it loses its Edge Port status becomes a normal spanning-tree port.


Non-Edge Ports

• Root Port

– The one switch port on each switch that has the best root path cost to the root.

• Point-to-Point Port (Link Type)

– Port operating in full-duplex mode.

– Connects to another switch and becomes a Designated Port.

– Uses a quick handshake with neighboring switch rather than timers to decide port state.

• Shared Medium Port (Link Type)

– Port operating in half-duplex mode.

– It is assumed that the port is connected to shared media where multiple switches might exist.


Point-to-Point: The Quick Handshake

• Switch A is connected to Switch B through a point-to-point link, – All ports are in the Discarding (Blocking) state.

• Switch A has a lower BID than Switch B. • Switch A sends a proposal message (Configuration BPDU) to Switch B,

proposing itself as the Root Bridge and the designated switch on the segment. • Switch B:

– Selects its new root port the port from which the proposal message was received and immediately goes into Forwarding State

– Forces all nonedge ports to the Discarding (Blocking) state, – Sends an agreement message.

• Switch A: Immediately transitions its designated port to the forwarding state.

• No loops in the network are formed because Switch B blocked all of its nonedge ports and because there is a point-to-point link between Switches A and B.

A B

Proposal

Agreement

RootDP RP


• Switch C is connected to Switch B: a similar set of handshaking messages are exchanged.

• Switch C selects the port connected to Switch B as its root port, and both ends immediately transition to the forwarding state.

• Handshaking process continues throughout topology.

A B

C

A B C

Proposal

Agreement

RootDP RP

A B

Proposal

Agreement

Root DP RPDP DP

D

Proposal

DP RPDP DPRP RPRoot

Agreement


RSTP Topology Change Notifications

• 802.1D– Switch detects a state change (up or down), it sends the Root Bridge a TCN BPDU.– The Root Bridge sends out a Configuration BPDU (TCN bit set) to all switches to

tell them about the change. (30 seconds before Forwarding)• RSTP

– Detects a topology change only when a nonedge port transitions to the Forwarding State.

– RSTP uses its convergence mechanisms (Edge Ports, Point-to-Point ports, handshaking, etc.) to prevent bridging loops.

– Therefore, topology changes are detected only so MAC address tables can be updated and corrected.

– This means that a loss of connectivity is not considered as a topology change any more, contrary to 802.1D (that is, a port that moves to blocking no longer generates a TC).

802.1D 802.1D


RSTP Topology Change Notifications

• When a bridge receives a BPDU with the TCN bit set from a neighbor: – It clears the MAC addresses learned on all its ports, except the one the port that

it receives the topology change. – It sends BPDUs with TCN set on all its designated ports and root port (RSTP no

longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified).• This way, the TCN floods very quickly across the whole network - now a one step

process. • The initiator of the topology change floods this information throughout the network,

as opposed to 802.1D where only the root did. • Much faster than the 802.1D equivalent < wait for the root bridge to be notified, and

then max age plus forward delays>. • In just a few seconds, or a small multiple of hello-times, most of the entries in the

CAM tables of the entire network (VLAN) flush. • This approach results in potentially more temporary flooding, but on the other hand it

clears potential stale information and allows rapid convergence.

RSTP

• When a topology change occurs:– Switch flushes the MAC addresses associated

with all nonedge ports. – Switch sends BPDU with TCN bit set to all

neighbors so they can update their MAC Address tables too.

RSTP no longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified


Rapid PVST Implementation Commands

Switch(config)# spanning-tree mode rapid-pvst

Cisco implements RSTP with Rapid PVST+

Switch(config)# spanning-tree mode pvst

• To revert back to the default PVST+ using traditional 802.1D:



Switch(config-if)# spanning-tree portfast

Cisco implements RSTP with Rapid PVST+

• RSTP automatically decides if a port is point-to-point link operating in full duplex or half-duplex.

• If you need to set it manually, other switch is in Half-Duplex but still point-to-point (by the way, both ends must then be Half-Duplex):

Switch(config-if)# spanning-tree link-type point-to-point

• To configure an RSTP edge port:



Access1# show spanning-treeVLAN0001 Spanning tree enabled protocol rstp Root ID Priority 24577 Address 0001.C945.A573 Cost 4 Port 26(GigabitEthernet1/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0003.E461.46EC Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 20



802.1D creates a single instance of STP for all VLANs.

PVST+ and RPVST create a single instance of STP for each VLAN.

If there are 500 VLANs in the network that would be 500 instances of STP running!

PVST+ does allow different VLANs to have different Root Bridges which can allow for the use of redundant links.


Multiple Spanning Tree Protocol – 802.1s

• MSTP is also known as Multiple Instance Spanning Tree Protocol (MISTP) on Cisco Catalyst 6500 switches and above


Multiple Spanning Tree Protocol – 802.1s

• Multiple Spanning Tree (MST) extends the IEEE 802.1w RST algorithm to multiple spanning trees.

• The main purpose of MST is to:– Reduce the total number of spanning-tree instances to match the physical topology

of the network – Thus reduce the CPU cycles of a switch.

• Allows the network administrator to configure the exact number of instances.• PVST+ runs a single instance of STP for each VLAN and does not take into

consideration the physical topology. – May have 1,000 VLANs but only 2 different topologies (2 different Root Bridges).– PVST+ will still create 1,000 instances of STP

• MST, on the other hand, uses a minimum number of STP instances to match the number of physical topologies present.

– May have 1,000 VLANs but only 2 different topologies (2 different Root Bridges).– MST will let you specify only 2 instances of STP.

Instance 1 maps to VLANs 1–500Instance 2 maps to VLANs 501–1000


MST Regions

• MST Region is a group of switches placed under a common administration (like an AS).

• In most networks a single MST region is sufficient.– A single MST Region can handle 15 STP instances (topologies).

• Within a region, all switches must run the instance of MST as defined by:– MST configuration name (32 characters)– MST configuration revision number ( 0 to 65,535)– MST instance-to-VLAN mapping table (4,096 entries)

• MST was designed to work with all forms of STP.

• IST (Internal Spanning Tree) instance runs to work out a loop-free topology inside the MST Region.

• IST presents the entire MST region as a single virtual switch (bridge) to the CST (802.1D) outside.

MST Region

802.1D 802.1D


MST

• Remember, the whole idea of MST is to map multiple VLANs to a smaller number of STP instances.– Cisco supports a maximum of 16 MST Instances (MSTIs) in a region.– The IST uses MST 0 leaving 1 through 15 available for use.

• The Distribution1 switch is the primary root bridge for the data VLANs 10, 30, and 100 – Secondary root bridge for the voice VLANs 20, 40, and 200.

• The Distribution2 switch the primary root bridge for the voice VLANs 20, 40, and 200 – Secondary root bridge for the data VLANs 10, 30, and 100.

• Distribution1 is chosen as CIST regional root. – It means that Distribution1 is the root for IST0.


MST

Distribution1(config)# spanning-tree mode mstDistribution1(config)# spanning-tree mst configurationDistribution1(config-mst)# name region1Distribution1(config-mst)# revision 10Distribution1(config-mst)# instance 1 vlan 10, 30, 100Distribution1(config-mst)# instance 2 vlan 20, 40, 200Distribution1(config-mst)# exitDistribution1(config)# spanning-tree mst 0-1 root primaryDistribution1(config)# spanning-tree mst 2 root secondary

Enables MST

Configure Region and MST instances

Configure Root Bridge


MST

Distribution2(config)# spanning-tree mode mstDistribution2(config)# spanning-tree mst configurationDistribution2(config-mst)# name region1Distribution2(config-mst)# revision 10Distribution2(config-mst)# instance 1 vlan 10, 30, 100Distribution2(config-mst)# instance 2 vlan 20, 40, 200Distribution2(config-mst)# exitDistribution2(config)# spanning-tree mst 2 root primaryDistribution2(config)# spanning-tree mst 0-1 root secondary

Enables MST

Configure Region and MST instances

Configure Root Bridge


MST

• For complete configurations go to:

• Configuration example to migrate Spanning Tree from PVST+ to MST

• http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml

http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a00807b075f.shtml


MST

Switch# show spanning-treeMST00 Spanning tree enabled protocol mstp Root ID Priority 24577 Address 0001.C945.A573 Cost 4 Port 26(GigabitEthernet1/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0003.E461.46EC Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 20

Enhancements to 802.1D, PVST+, EtherChannel, RSTP and MST

CIS 187 Multilayer Switched Networks

CCNP SWITCH

Rick Graziani