rstp vs stp

RSTPRSTP

vs

STPSTP

Instructors :

Assoc’ Prof’ Reuven Cohen

Mr. Itay Dabran

Mr. Mordo Shalom

Submitting :

Danny Kalmar 01702821-8

Gilad Wallach 03279719-3

Omer Sharabi 03385662-6

AgendaAgenda Project Definition

Implementation

Test Plan

Results

Main Conclusions

General Observations

AgendaAgenda Project Definition

ImplementationImplementation

Test PlanTest Plan

ResultsResults

Main ConclusionsMain Conclusions

General ObservationsGeneral Observations

IntroductionIntroduction

Why do we need spanning tree bridges?

At the beginning : 802.1d

But : the rules were changed

RSTP as an evolution of STP.

Goals Goals

Implementing STP and RSTP

Comparing between the performances of the protocols

Results’ discussion.

AgendaAgenda Project DefinitionProject Definition

Implementation

Test PlanTest Plan

ResultsResults



S/W ModulesS/W ModulesGeneral:

We implemented a simulation which runs both protocols over a variety of randomized nets

It can run several tests in a single execution and collect statistics about the building and recovery abilities of each protocol

Simulation’s parameters : num’ of bridges and lans , num’ of tests and failures within each test, bridge’s configuration and packet’s lost probability.

The Net Manager Module

Simulation’s main loop

Main features : Creation and initialization of new a randomized net

Running the bridges protocols using the net’s members’ interfaces and the given parameters

Detection of the tree’s : building , failing and recovering

The ability to run multiple tests and failures on a given configuration

Statistics collecting.

The Bridge Module

Supports both protocols due to the mode of operation

Main features for the 802.1W: RSTP’s BPDUs mechanism

Rapid Transition to Forwarding State

Proposal / Agreement mechanism

Sync Mechanism

Uplink Fast

RSTP’s Topology Change Detection and Propagation

Main features for the 802.1D: STP’s BPDUs mechanism

STP’s Topology Change Detection and Propagation

The LAN Module

Main features : Distribution of BPDUs from the previous cycle to their destinations

The LAN receives all messages and prepare them to be sent out the next cycle.

The Testing Module

Main features : Generation of failures on demand : disconnection of a forwarding port or connection of a disabled port while keeping the net with connectivity

Maintenance of failures’ list in order to support running the same tests for both protocols .

System ArchSystem ArchBridge.Tick()

Lan.Tick()

TestCreateFailure()

send_bpdu

rece

ived

_bpd

u

NetManager

Testing

LAN

Bridge

Main Loop (1)Main Loop (1)Case: - Packets’ lost probability != 0

For all tests :

• Set a randomized net

• Run each protocol till its tree become stable

• Collect test’s results.

Print statistics.

Main Loop (2)Main Loop (2)Case: - Packets’ lost probability = 0

For all tests :

• Set a randomized net

• Run each protocol till its tree become stable

• Collect initialization’s results

• For all failures :

Activate the failure

Run each protocol till its tree recover

Collect recovery’s results.

Print statistics.



Test Plan

ResultsResults



Test’s ParametersTest’s Parameters

All the net’s member possibilities are represented as a pair of (Bridge_Num , LAN_Num ) :

• Dense networks : { (2,6), (5,10) , (8,15) ,(10,17) , (12,25) , (15,30) }

• Sparse networks : { (2,2), (5,5) , (8,8) ,(10,10) , (12,12) , (15,15)}

Bridge’s parameters (following the Cisco configuration) :

• Forward delay = 15000 ticks

• Max age = 20000 ticks

• Hello time = 2000 ticks.

Performance's CriteriaPerformance's CriteriaCase: - Packets’ lost probability = 0 :

• Average Initialization time

• Average number of BPDUs’ that were sent during initialization

• Average recovery time

• Average number of BPDUs’ that were sent during recovery

Case: - Packets’ lost probability =! 0 :

The same without the recovery information



Test PlanTest Plan

Results



Recover Time In Sparse Networks

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Recover Time in Sparse NetworksRecover Time in Sparse Networks

Immediate conclusions:Immediate conclusions:

RSTP recovers much faster than STPRSTP recovers much faster than STP

Recover Time In Dense Networks

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NumBridges NumLans 2 6 5 10 8 15 10 17 12 25 15 30

Recover Time in Dense NetworksRecover Time in Dense Networks


RSTP recovers much faster than STPRSTP recovers much faster than STP

Recover time is similar to that in sparse networks.Recover time is similar to that in sparse networks.

Num of BPDU In recover In Sparse Networks

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Nu

m B

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W Num of BPDU

BPDUs Num sent during Recovery Time in BPDUs Num sent during Recovery Time in Sparse NetworksSparse Networks


RSTP requires less BPDU to achieve stabilityRSTP requires less BPDU to achieve stability

This is caused mainly because the recovery time is This is caused mainly because the recovery time is much faster .much faster .

Num of BPDU In recover In Dense Networks

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D Num of BPDU

NumBridges NumLans 2 6 5 10 8 15 10 17 12 25 15 30

BPDUs Num sent during Recovery Time in BPDUs Num sent during Recovery Time in Dense NetworksDense Networks

Graph Explanation:Graph Explanation:

RSTP requires less BPDU to achieve stabilityRSTP requires less BPDU to achieve stability

Dense network requires much more BPDUs to Dense network requires much more BPDUs to stabilize. stabilize.



Test PlanTest Plan

ResultsResults

Main Conclusions


ConclusionsConclusions Recovery – RSTP recovers significantly faster than STP , less significantly better in BPDUs count

Dense and Sparse networks – We did not find any critical differences except the expected gap between BPDUs count

Packet Lost Probability – both protocols act as usual as long as the the probability is less than 10%. Both protocols stability is not guaranteed over ~60%.



Test PlanTest Plan

ResultsResults


General Observations

ObservationsObservations The uplink fast feature in the RSTP can improve if it will use the “Back Up” port feature in addition to the “Alternate” port feature

RSTP’s initialization’s performances can be increased significantly through appropriate configuration (“slow” transition avoidance)

Attention to the fact that RSTP recovers faster than STP which is a very important thing in today networks. RSTP “pays” in increased BPDUs count which is less important due to today possible band width.

Additional tests could explore more deeply the affects and the exact legal range of values of Packet Lost Probability for each protocol .

Old FoilsOld Foils

INITIALIZATION TIME IN NOT BUSY NETWORKS

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0246810121416


cycl

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D Initilalization time with fd 3

W initialization with fd 3

D Initilalization time with fd 10


D initialization with fd 20

W Initilalization time with fd20

Initialization Time in not busy NetworksInitialization Time in not busy Networks


Similar initialization times in medium and large size Similar initialization times in medium and large size Networks,with slight advantage to the RSTP protocolNetworks,with slight advantage to the RSTP protocol

In small Networks RSTP builds the tree much fasterIn small Networks RSTP builds the tree much faster

As expected, a long Forward Delay lengthens the As expected, a long Forward Delay lengthens the initialization time.initialization time.

INITIALIZATION TIME IN BUSY NETWORKS

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Bridge Num

cycl

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# Bridges # Lans

2 6 5 10 8 15 10 17 12 25 15 30

Initialization Time in busy NetworksInitialization Time in busy Networks


Similar initialization times in medium and large size Similar initialization times in medium and large size Networks,with slight advantage to the RSTP protocolNetworks,with slight advantage to the RSTP protocol

In small Networks RSTP builds the tree much fasterIn small Networks RSTP builds the tree much faster

As expected, a long Forward Delay lengthens the As expected, a long Forward Delay lengthens the initialization time.initialization time.

Initialization time is similar to that in not busy Initialization time is similar to that in not busy networks.networks.

RECOVER TIME IN NOT BUSY NETWORKS

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num bridges=num lans

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W recover with fd 3

D recover with fd 10

W recover with fd 10



RECOVER TIME IN BUSY NETWORKS

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W recover with fd 3





# Bridges # Lans

2 6 5 10 8 15 10 17 12 25 15 30

BPDU NUM IN INITIALIZATION IN NOT BUSY NETWORKS

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Nu

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BPDUs Num sent during Initialization Time BPDUs Num sent during Initialization Time in not busy Networksin not busy Networks


Linear growth in bpdu sent during initialization in Linear growth in bpdu sent during initialization in relation to the network size in both protocolsrelation to the network size in both protocols

RSTP sends much more BPDUs because of levels RSTP sends much more BPDUs because of levels of distribution.of distribution.

BPDU NUM IN INITIALIZATION IN BUSY NETWORKS

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Bridges Num

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#Bridges #Lans 2 6 5 10 8 15 10 17 12 25 15 30

Bpdus Num sent during Initialization Time in Bpdus Num sent during Initialization Time in busy Networksbusy Networks


Linear growth in bpdu sent during initialization in Linear growth in bpdu sent during initialization in relation to the network size in both protocolsrelation to the network size in both protocols

the gap between the number of BPDUs in RSTP and the gap between the number of BPDUs in RSTP and STP is not as big in busy networks.STP is not as big in busy networks.

BPDU NUM IN RECOVER IN NOT BUSY NETWORKS

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Bridge Num=Lan Num

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BPDU NUM IN RECOVER IN BUSY NETWORKS

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Bridge Num

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#Bridges #Lans 2 6 5 10 8 15 10 17 12 25 15 30

rstp vs stp

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