STP/BPDU/MST/PVST/RSTP Flashcards
what are the 5 STP port roles?
root, designated, blocking, alternate, forwarding (host)
what does Root Guard do?
controls where candidate root bridges can be connected and found on a network
How does Root Guard work?
a port can only forward or relay BPDUs, but can’t receive them, disabled by default, enabled per-port, blocks port when superior BPDUs are received
How is Root Guard used?
on ports where you never expect to find a root bridge for a VLAN
What is BPDU Guard?
if any BPDU is received on a port, it puts the port into the errdisable state
How can BPDU Guard be configured?
globally or per-port
What does Loop Guard do?
tracks BPDUs on nondesignated ports. When those BPDUs stop coming, the port is put into loop-inconsistent state and blocks
How does loop guard block ports?
only for the offending VLAN on the port
What does BPDU filtering do?
effectively stops STP on filtered ports
Where is root guard enabled?
all ports where root isn’t expected
where is BPDU guard enabled?
all user ports that have portfast enabled
where is loop guard enabled?
all nondesignated ports, but ok for all ports
can root guard and loop guard be used together
no
can root guard and BPDU guard be used together?
no
should BPDU guard and BPDU filter be used together?
no
RSTP uses which standard?
802.1w
What are the RSTP port roles?
root, designated, alternate, and backup
RSTP root port
port with best root path cost
RSTP designated port
Port with best root path cost on segment
RSTP alternate port
port with alternative path to root less desirable than root
RSTP backup port
port with redundant, but less deisrable connection to a segment. Possibly root candidate
What are the RSTP port states?
discarding, learning, forwarding
RSTP discarding state
incoming frames are dropped (combination of disabled, blocking, and listening)
RSTP learning state
incoming frames dropped, but MACs learned
RSTP forwarding state
frames are forwarded
RSTP BPDU structure
some unused bits are used to allow a port to identify its role and state. Also the BPDUs state that they are V2 BPDUs
When are RSTP BPDUs sent?
every hello interval regardless of whether BPDUs are received from root, allowing any switch to take an active role maintaining the topology
What if RSTP BPDUs aren’t received?
If three are missed in a row, the neighbor is considered down and the data for that neighbor is aged
What is the RSTP default hello interval?
2 seconds
What happens if both 802.1D and RSTP BPDUs are received?
the port will operate under 802.1D rules. If they are received on the same port, it will run 802.1D until the migration delay expires
What are the steps of RSTP convergence?
1- root bridge is elected, 2-the state of every switch port in the STP domain must be brought from blocking state to the appropriate state
What are the 3 RSTP port types?
edge, root, and point to point
RSTP edge port
only a single host connects . If one BPDU is received, it is no longer an edge port
RSTP point to point port
port that connects to another switch and becomes a designated port
How are RSTP point to point ports determined?
automatically by duplex mode in use. Full duplex are point ot point. Half duplex ports use traditional 802.1D convergence is used.
How is RSTP synchronization accomplished?
all non-edge ports are discarding. After the root bridge is identified, the port with superior BPDU becomes root
How does RSTP converge?
if a proposal is received, the recipient isolates, all nonedge ports blocked until proposal sent causing neighbors to synch, which propagates out in waves
How does RSTP identify a topology change?
only when a nonedge port transitions to forwarding
How is an RSTP edge port configured
with portfast
What is RPVST+?
an instance of RSTP running for each VLAN on the switch. Changing from PVST to RPVST+ is disruptive
When looking at the sh spanning tree output, what does P2P denote?
a point to point port type
When looking at the sh spanning tree output, what does P2P peer(STP) denote?
a point to point port type but the neighboring device runs traditional 802.1D STP
What does MSTP do?
Used when there are 1 or more VLANs mapped to a single STP instance
What do you need to determine to use MSTP?
the number of STP instances needed to support the desired topologies and whether to map a set of VLANs to each instance
Can MSTP interoperate with 802.1q and/or PVST+?
yes to both
What does MSTP consist of?
regions and instances
How is an instance defined?
by name, config revision, and instance to vlan mapping table
What is an IST instance?
within a single MST region, an IST instances runs to work out a loop free topology between links where CST meets the region boundary and all switches in the region. It runs at the boundary.
What is an MST instance?
The MST instance (MSTI) runs alongside the IST and represents an STP instance
How many MST instances can be in a region?
16 - IST gets MSTI 0, 1-15 are available for use. MSTIs are locally significant to the MST region
How do you implement MST?
MST attributes must be manually entereed on each switch in the region. They don’ t propagate like VTP.
What are the steps to configure MST?
1- enable MST, 2-enter MST config mode, 3-assign region name and region configuration rev, 4-map vlans to an MSTI, 5-show pending changes, 6- commit by exiting
What is the IEEE standard for STP?
802.1D
How are BPDUs spread?
multicast to 01-80-c2-00-00-00
What are the 2 types of BPDU?
configuration and TCN
How often are BPDUs sent?
2 seconds (def)
What is a bridge ID made up of?
bridge priority and MAC
What is the bridge priority range?
0-65535 (def 32768) lower=better
In a converged fabric, which switch(es) send config BPDUs?
root
How is root port decided upon?
lowest cumulative cost to root
What is the cost of a 10 Mbps link?
100
What is the cost of a 100Mbps link?
19
What is the cost of a 1Gbps link?
4
What is the cost of a 10Gbps link?
2
How many designated ports are there?
1 per segment
If there are 2 ports with same root cost, how is the tie broken for designated port?
1-lowest root bridge ID, 2-lowest root path cost, 3-lowest bridgeID, 4-lowest port ID
What are the 5 STP states?
disabled, blocking, listening, learning, forwarding
What is the STP disabled state?
admin down
What is the STP blocking state?
Can hear only BPDUs
what is the STP listening state?
can send and receive BPDUs
What is the STP learning state?
after forwarding delay, port can learn new MAC addresses
What is the STP forwarding state?
after another forwarding delay, the port can send and receive data frames, collect MAC addresses, and send and receove BPDUs
What are the 5 steps to manualy configure STP?
1-ID link path costs, 2-ID roodt bridge, 3-select root port (1/switch), 4-select designated port (1/segment), 5-ID blocking port
What is the STP hello timer?
Time between BPDUs sent by root bridge. Default of 2 seconds
What is the STP forward delay timer?
The time that a port spends in both listening and learning states . Default 15 seconds
What is the STP Max Age timer?
The time interval that a switch stores a BPDU before discarding it. Default 20 seconds
What is the default network diameter?
7 switches from root bridge
Where should you change the network diameter value?
Cisco recommends only on the root bridge
What is a topology change?
When a port moves into forwarding or from fowarding or learning to blocking.
What happens when the topology changes?
A TCN BPDU is sent out of the switch’s root port. The switch will continue sending TCN’s every hello interval until ack’d by upstream neighbor. The root bridge will send a Config BPDU to all switches
What happens when switches receive a configuration BPDU?
They shorten their bridge table aging times from default (300sec) to the fowarding delay (15 sec)
What is a direct topology change?
One that can be detected on a switch interface (ie. Up/down)
What is an indirect topology change?
The link status stays up, but something between them has failed or is filtering traffic
What is an insignificant topology change?
A host port goes up or down
What is common spanning tree (CST)?
Single instance of STP for all VLANs. BPDUs are sent over trunks using the native VLAN with untagged frames. Dot1q based
What is Per VLAN STP (PVST)?
Cisco proprietary. 1 instance of STP/VLAN. Requires ISL instead of dot1q
What is PVST plus (PVST+)?
allows devices to interoperate with PVST and CST. Can use both dot1q and ISL
What is the port ID?
16 bits (8b port priority, 8b port number)
what is the port number range?
0-255
what is the port priority range?
0-255 (lower is better)
Where should STP timers be configured and why?
on root, because the root bridge propagates timers with config BPDU
How do you automatically configure STP timers
use the spanning-tree root macro
What is portfast?
almost eliminates listening and learning states for single hosts on an access link
What does the switchport host macro do?
enables portfast, sets the port to access and disables PAgP
What does uplinkfast do?
enables switches at the end of the spanning tree branches to have a functioning root port while keeping 1 or more redundant potential ports in blocking mode. When the main fails, the other comes up.
What are the gotchas for uplinkfast?
should be used on access switches, can’t be used on root, keeps enabled switch from becoming root by raising priority of switch and all ports, making them undesirable
How does uplinkfast handle changes in topology?
notifies upstream neighbors by sending multicasts on behalf of hosts at the interval of the max update rate parameter.
What is backbonefast?
causes switch to actively determine whether alternative paths exist to root bridge in case ther eis an indirect failure
How does backbonefast determine whether alternative paths exist?
1- inferior BPDU on blocked-considered alternative, 2-inferior on root-all blocked ports considered alternate, 3-if inferior arrives on root and no blocked ports, assumes loss of connectivity to root
What is a root link query (RLQ)?
backbonefast uses RLQ to determine if upstream switches have stable connections to root bridge
How does backbonefast work?
by short-circuiting the max age timer
How should backbonefast be configured?
on all switches in network to enable RLQ request and reply
When are new path costs from BPDUs computed on a switch?
when the BPDU comes IN the switch.
When is the UplinkFast command not allowed?
On the root bridge switch.
What are the 5 STP port states?
Disabled-Blocking-Listening-Learning-Forwarding
What is the STP Max Age timer?
The time that a switch stores a BPDU before discarding it. Default is 20 seconds. Range is 6-40
Define STP PVST.
Per-VLAN Spanning Tree. Cisco Proprietary, and operates a separate instance of STP on each VLAN. Requires ISL encapsulation between switches. PVST and CST cannot easily coexist.
How many root ports can a single switch have?
Only ONE, that always points towards the root bridge!
If a switch has BackboneFast and any blocked ports, what does it use to figure out alternate paths?
The Root Link Query (RLQ) protocol.
What is the STP path cost of 10G, 1G, 622M, 155M, 100M, and 10M?
2, 4, 6, 14, 19, and 100
What is the value range and default value of STP port priority?
0-255, and defaults to 128.
When should you use STP PortFast?
Only from access layer switches to workstations.
When are new path costs from BPDUs computed on a switch?
when the BPDU comes IN the switch.
When is the UplinkFast command not allowed?
On the root bridge switch.
What are the 5 STP port states?
-Disabled-Blocking-Listening-Learning-Forwarding
What is the STP Max Age timer?
The time that a switch stores a BPDU before discarding it. Default is 20 seconds. Range is 6-40
Define STP PVST.
Per-VLAN Spanning Tree. Cisco Proprietary, and operates a separate instance of STP on each VLAN. Requires ISL encapsulation between switches. PVST and CST cannot easily coexist.
How many root ports can a single switch have?
Only ONE, that always points towards the root bridge!
If a switch has BackboneFast and any blocked ports, what does it use to figure out alternate paths?
The Root Link Query (RLQ) protocol.
What is the STP path cost of 10G, 1G, 622M, 155M, 100M, and 10M?
2, 4, 6, 14, 19, and 100
What is the value range and default value of STP port priority?
0-255, and defaults to 128.
When should you use STP PortFast?
Only from access layer switches to workstations.
When a link goes down in STP, what is the total down time of that device based off of? / calculated from?
- The max-age timer (20 seconds)2. The Hello timer (2 seconds)3. The forwarding delay for both listening and learning (15 seconds x2!)
What is the command to enable UplinkFast on a switch and set the max-update-rate? Also what is the ranges and purpose of this command?
(config)spanning-tree uplinkfast max-update-rate #####This limits how often the device will send multicast messages on fail-over, and the range is 0-65535
What are the three STP timers?
Hello time, Forward Delay, and Max Age
The cumulative cost of all the links leading to the root bridge is called the _______?
root path cost.
What macro command enables PortFast, sets the port to access, and disabled PAgP?
(if)switchport host
What is the STP Forwarding Delay?
The time that a switch port must spend in the listening and learning states before advancing to the forwarding state. Default is 15 seconds. Range is 4-30
What is a root bridge?
The root bridge is the bridge with the lowest Bridge Priority value, or the lowest MAC is all values are equal. It has no disabled(blocking) ports.
What are the three main types of STP?
CST (common spanning tree), PVST (Per-VLAN spanning tree), and PVST+
What are the 4 tie-breaking STP decisions?
- Lowest Bridge ID2. Lowest root path cost to root bridge3. Lowest sender bridge ID4. Lowest sender port ID
In STP, a value of 0 on the max-update-rate parameter for UplinkFast means what?
It means that no multicast messages will be sent on fail-over.
When should you use STP UplinkFast?
Only from access layer switches to distro layer switches when there are dual uplinks.
When does STP acknowledge that a topology change has occurred?
When a port goes up or down, usually any port going to the forwarding state, or a port going to the blocking state.
What is the correct terminology for a Spanning-Tree Loop?
A Bridging Loop.
How much extra delay time is added to the default spanning tree process of 30 seconds when a PAgP Etherchannel link in configured for STP?
An extra 20 seconds. This brings the total negation time to 50 seconds.
What command enables all ports configured for Access mode to use PortFast?
(config)spanning-tree portfast default
How can you change the network diameter value in STP?
add ‘diameter #’ to the end of the command ‘spanning-tree vlan # root primary’
In STP extended system-id, bridge priority can range from 0-61440 but only in multiples of _____?
4096
Will a lower value or higher value make a switch the root bridge?
Lower Bridge Priority/MAC
Can BPDUs be shared by CST and PVST?
Never, as they require different trunking methods.
What configuration will cause a TCN BPDU to NOT be sent when a topology change occurs?
spanning-tree PortFast on the interface.
What is the STP hello timer?
the time between Configuration BPDUs sent by the root bridge. Default is 2 seconds. Range is 1-10
Explain the ‘Disabled’ port state in STP.
a port that is administratively shut down by an administrator or by the system because of a fault.
If an RLQ reply is received on a root port, what does this mean? A non-root port?
-That the path to the root bridge is in tact and stable. -Non-root: that a new path must be chosen.
Will an STP bridge priority value of 0 work?
Not with the automatic method. Only with the manual method.
What is the default forward delay timer?
15 seconds.
What happens when you change a STP timer on the root bridge?
It propagates all three timer values throughout the network with the BPDUs.
Explain the ‘Listening’ port state in STP.
This port can only send and receive BPDUs. Because of this it is allowed to become a root or designated port.
What are the two types of BPDUs, and define their use.
-Configuration BPDU, used for Spanning Tree computation.-Topology Change Notification (TCN) BPDU, used to announce changes in the network topology.
What is an indirect link failure in STP, and how does a switch detect them?
It occurs when a link that is not directly connected to a switch fails. It is detected whenever a switch starts receiving inferior BPDUs from its designated bridge on the root or blocked ports.
What command set the bridge priority for STP?
(config)spanning-tree vlan ## priority #####
What is a BPDU?
a Bridge Protocol Data Unit. It is a data message that is exchanged between switches to support the Spanning Tree Protocol.
What does the ‘spanning tree vlan # root secondary’ command do?
It sets the bridge priority to 28672. This is less than the default 32768, but more than the ‘primary’ keyword of 24576
Where is the ideal placement of the pri/sec root bridge?
Near the center of the Layer 2 network on a powerful switch.
Explain the ‘learning’ port state in STP.
After the ‘forward delay’ from the listening state, it becomes a learning state. This port can still send and receive BPDUs, but can also now learn new MAC addresses.
Explain the ‘Blocking’ port state in STP.
Ports start in this state. This port cannot send or receive data and cannot add MAC addresses to its table. It can only receive BPDUs.
What is contained in the STP Port ID?
8-bits for the Port Priority and 8-bits for the Port Number.
Define STP CST.
Common Spanning Tree. Based on IEEE 802.1Q when all BPDUs are transmitted over the native VLAN with untagged frames.
TCN BPDUs are send out what port?
The switches root port.
By default, how often are BPDUs sent?
Every 2 seconds.
When should you use STP BackboneFast?
Enables faster convergence on core layer switches after changes occur.
What is a secondary root bridge used for and how do you configure one?
It is used in case the primary root bridge goes down you can engineer its replacement. Simply make another switch have a value lower than the default but higher than the primary root.
When are inferior BPDUs send in STP?
When a designated bridge loses connectivity to the root bridge, making it advertise itself as the new root.
What are the 5 steps to manual STP computation?
-ID path costs on all links.-ID a root bridge.-Select root ports (1 per switch)-Select designated ports-ID blocking ports.
What is the default bridge table aging timer?
300 seconds.
What command will allow you to see the spanning tree Port Cost value of an interface?
(priv)show spanning-tree interface TYPE MOD/NUM cost
What happens to a PortFast port that receives a BPDU?
It immediately enters the blocking state.
What is the value range and default value for bridge priority?
0-65535, defaults to 32768(0x8000)
Explain the ‘Forwarding’ port state in STP.
After another forwarding delay from the learning state, the port is now a fully functioning port, and can send and receive all data.
Where should UplinkFast be used?
On leaf-node switches, or switches on the ends of spanning tree branches.
What is the well-known multicast address that BPDUs are sent to?
01-80-c2-00-00-00
If you use BackboneFast, what switches should it be used on?
It should be used on ALL switches on the network because of the RLQ request and reply process.
define PVST+
PVST plus. Allows all devices to operate with CST, PVST, and PVST+. It operates over both ISL and 802.1Q
What does the ‘spanning tree vlan # root primary’ command do?
It makes the switch attempt to become the root bridge. If the current root bridge priority is more than 24576, it sets its priority to 24576. If the current root bridge is less than that, it sets its priority to 4096 less than the current root.
What is a designated port in Spanning Tree?
A port where only BPDUs with HIGHER root path costs are received. This means the that the other switch attached to that port is using that port as a root port! This port should stay online!
What command sets the STP port priority on a switch port?
(if)spanning-tree vlan ## port-priority ###(lower is better!)
What multicast address is sent to by UplinkFast when a new link comes up, and what is sent?
0100.0ccd.cdcd -It sends all of the MAC addresses in the bridging table as the source address to update upstream devices.
What does the UplinkFast command do to a switch?
It keeps one functioning root port and one or more potential root ports in blocking mode. When that primary root port fails, another blocked potential root port immediately comes up. It also changes the bridge priority to 49152 and increases all path costs by 3000.
What does BackboneFast do to the Max-Age Timer on a switch?
It short-circuits the max age timer, and reduces the convergence delay from 50 to 30 seconds.
What is the range for network diameter in STP?
1-7, default is 7.
What is the IEEE standard for RSTP?
802.1w
How do you enable/disable BPDU filtering on a per-port basis?
(if)spanning-tree bpdufilter [enable, disable]
What is the IEEE standard for MST?
802.1s
What does BPDU guard do to a switchport?
If a BPDU is received on a port with BPDU guard, it is immediately placed into the errDisabled state.
What does BPDU filtering do?
It effectively disables STP on a switchport.
Can a switch run both MST and PVST+ at the same time?
No! MST relies on the RSTP configuration to operate, and therefor, cannot use PVST+.
What does Loop Guard do to switch ports?
It monitors BPDU activity on non-designated ports. When BPDUs go missing, Loop Guard moved the port into a loop-inconsistent state. When BPDUs are received again, the port progresses automatically through the STP states and becomes active.
Are the following configuration combinations permissible on a switch port?Root guard and UDLD
Permissible!
RSTP uses what BPDU version?
version 2.
How many MSTIs can exist in a single MST region?
- The IST is always MSTI 0, and that leaves MSTI 1-15 open for use.
What type of message does RSTP send when negotiating convergence?
It sends a proposal!
Are the following configuration combinations permissible on a switch port?Root guard and BPDU guard
NOT-Permissible!
What is the relationship between PortFast and BPDU guard?
All ports with PortFast have BPDU guard enabled by default.
How can you globally enable BPDU filtering on all PortFast ports?
(config)spanning-tree portfast bpdufilter default
In RSTP, non-edge ports begin in what RSTP state?
The RSTP discarding state.
What does RSTP assume with regard to duplex settings?
That full-duplex links are Point-to-Point and half-duplex links fall back to CST.
When should STP Root Guard be used?
On switchports where you never expect to find the root bridge for any VLAN.
Within MST what is an IST?
Internal Spanning Tree, it is a locally significant CST bounded by the edges of the MST region.
In RSTP how often are BPDUs exchanged?
The default hello timer in RSTP is 2 seconds.
What does the ‘spanning-tree link-type point-to-point’ command accomplish?
It forces a RSTP port to be point-to-point regardless of duplex settings.
When running MST, all switches must have what three identical attributes to be considered in the same region?
The same MST configuration name, revision number, and instance-to-VLAN mapping table.
What two STP features help detect or prevent the unexpected loss of BPDUs?
Loop Guard, and Unidirectional Link Detection (UDLD).
What ports should BPDU guard never be enabled on?
Switch uplinks where the root bridge is located.
Are the following configuration combinations permissible on a switch port?Root guard and Loop guard
NOT-Permissible!
What happens when a BPDU is received on a port with Root Guard configured?
It is placed in the blocking state, with a root-inconsistent state.
What are the 5 states a port can have after convergence in STP?
Root port, Designated port, Blocking port, Alternate port, and Forwarding port.
In MST, by default, what VLANs are mapped to the IST (MSTI 0)?
All of the VLANs are mapped to the IST by default. You must explicitly map them to another MSTI if needed.
Are the following configuration combinations permissible on a switch port?Loop Guard and UDLD
Permissible!
How to other MSTIs receive BPDU information in MST?
The MST BPDU is sent on the IST (MSTI 0) with a special M-Record appended to the BPDU.
How do you globally enable Rapid Per-VLAN Spanning Tree (RPVST+)
(config)spanning-tree mode rapid-pvst
According to RSTP, any port role can have what three possible states?
-Discarding, incoming frames are dropped, no MACs are learned.-Learning, only MACs are learned.-Forwarding, frames are forwarded according to learned frames.
What are the 5-steps to configuring MST on a single switch?
- spanning-tree mode mst2. spanning-tree mst configuration3. name NAME4. revision #####5. instance #ID# vlan #LIST#
Can RSTP coexist on a network with CST?
Yes, each versions BPDUs are compatible.
Give a quick explanation of where the following STP configurations should be used: Root guard, BPDU guard, Loop guard, UDLD.
-Root guard, Apply to ports where root is never expected.-BPDU guard, apply to all ports that have PortFast enabled.-Loop guard, Apply to non-designated ports, but ok to apply to all ports.-UDLD, Apply to both sides of all fiber links.
Even though loop-guard is configured on switch ports, it action is taken on a per-_____ basis.
per VLAN!
When does RSTP detect a topology change?
When a non-edge port transitions to the forwarding state.
What is the default message interval for UDLD?
15 seconds.
What are the three types of RSTP ports?
-Edge port, where only a single host connects.-Root port, has the best cost to the root.-Point-to-point, any port that connects to another switch and becomes a designated port.
In MST, what MSTI is allowed to send BPDUs?
Only the IST, on MSTI 0, us allowed to send BPDUs.
What is the IEEE standard for STP?
802.1D
How does CST work out a loop-free technology with MST?
It considers each MST region as a single ‘bridge’
When enabled globally, what ports does UDLD effect? How do you enable it?
Only Fiber-Optic ports. (config)udld [enable, aggressive, message time ###]
If a port is placed in the errDisabled state, what is the only way it can be re-enabled?
By being manually re-enabled, or waiting for the errDisabled timeout function.
What does *PVST* stand for?
Per VLAN Spanning Tree
What does IST stand for?
Internal Spanning Tree
What is IST?
IST is just another name for Instance-0.
How is an IST Master elected?
If CST Root bridge is elected inside MST region, CST root is the IST Master. However, if this is not the case, IST Master is the MST switch with the lowest cost to the CST.
By default, what is considered a dead neighbor in *PVST+*?
A neighbor is declared dead if the neighbor missed 10 BPDUs.
What does *RPVST+* stand for?
Rapid Per VLAN Spanning Tree
Why was *RPVST+* developed after *PVST+*?
RPVST was developed after PVST because state changes were too slow in the original STP. RPVST was designed to speed up convergence.
In RPVST+, what is a P2P link type?
In RPVST+, a P2P link type is a full duplex link. These links are able to do the P / A flag negotiations.
In *RPVST+*, what is a Shared link type?
In RPVST+, a Shared link type is a half duplex link.
What is a major change in *RPVST* compared to *PVST* in regards to BPDUs?
In PVST, Root Bridge was the only switch to create Configuration BPDUs. In RPVST, all switches generate their own Configuration BPDUs to act as keepalives for neighbors.
By default, what is considered a dead neighbor in *RPVST+*?
A neighbor is declared dead if the neighbor missed 3 BPDUs.
What is the *RSTP Discarding State*?
The RSTP Discarding state combines the 802.1d disabled, blocking, and listening states. No MAC addresses are learned and incoming frames are dropped.
What is the *RSTP Learning State*?
The RSTP Learning State can’t send or receive data but MAC addresses are learned.
What is the *RSTP Forwarding State*?
The RSTP Forwarding State can send or receive data.
What is the *RSTP Proposal Flag*?
The Proposal Flag in RSTP is enabled whenever a bridge requests to become the Root.
What is the *RSTP Agreement Flag*?
The Agreement Flag in RSTP is enabled whenever a bridge agrees with another bridge in regards to that bridge’s request to become Root.
