All Cisco-Network Study Notes: Frame Distribution on a Two-Link EtherChannel-Configuration BPDU Message Content-Basic Spanning Tree Operation

The Foundation Arbitrary is a accumulating of tables and abstracts that provides a acceptable review

of abounding key concepts in this chapter. For those of you already adequate with the capacity in

this chapter, this arbitrary could advice you anamnesis a few details. For those of you who aloof read

this chapter, this analysis should advice coalesce some key facts. For any of you accomplishing your final

preparation afore the exam, these tables and abstracts will hopefully be a acceptable way to

review the day afore the exam.

Table 5-6 Frame Administration on a Two-Link EtherChannel

Binary Addresses

Two-Link EtherChannel

XOR and Articulation Number

Addr1: ... xxxxxxx0

Addr2: ... xxxxxxx0 ... xxxxxxx0: Articulation 0

Addr1: ... xxxxxxx0

Addr2: ... xxxxxxx1 ... xxxxxxx1: Articulation 1

Addr1: ... xxxxxxx1

Addr2: ... xxxxxxx0 ... xxxxxxx1: Articulation 1

Addr1: ... xxxxxxx1

Addr2: ... xxxxxxx1 ... xxxxxxx0: Articulation 0

Table 5-7 EtherChannel Configuration Commands

Task CLI-Based Command IOS-Based Command

Assign EtherChannel

Distribution Method

set anchorage approach all distribution

{ip | mac}[source | destination | both]

port accumulation group-number

[distribution {source |

destination}]

View EtherChannel

Capabilities

show anchorage capabilities [module/port]

Configure EtherChannel set anchorage approach module/port-range

mode {on | off | adorable | auto}

port accumulation group-number

[distribution {source |

destination}]

Show EtherChannel appearance anchorage approach [mod[/port]] appearance anchorage accumulation [groupnumber]

Foundation Arbitrary 189

Table 5-8 Configuration BPDU Message Content

Field Description Cardinal of Bytes

Protocol ID (always 0) 2

Version (always 0) 1

Message Type (Configuration or Topology

Change Notification BPDU)

Flags 1

Root Bridge ID 8

Root Path Bulk 4

Sender Bridge ID 8

Port ID 2

Message Age (in 256ths of a second) 2

Maximum Age (in 256ths of a second) 2

Hello Time (in 256ths of a second) 2

Forward Adjournment (in 256ths of a second) 2

Table 5-9 Cartography Change Notification BPDU Message Content

Field Description Cardinal of Bytes

Protocol ID (always 0) 2

Version (always 0) 1

Message Type (Configuration or Topology

Change Notification BPDU)

Table 5-10 Basal Spanning Tree Operation

Task Procedure

Elect Basis Bridge Lowest Bridge ID.

Select Basis Anchorage (one per switch) Lowest Basis Path Cost.

Select Designated Anchorage (one per segment) Lowest Basis Path Cost.

Block ports with loops Block ports that are non-Root and non-

Designated Ports.

190 Affiliate 5: Redundant About-face Links

Table 5-11 Spanning Tree Tie Breaker Criteria

Sequence Criteria

1 Lowest Basis Bridge ID

2 Lowest Basis Path Cost

3 Lowest Sender Bridge ID

4 Lowest Anchorage ID

Table 5-12 STP Path Cost

Link Bandwidth Old STP Bulk New STP Cost

4 Mbps 250 250

10 Mbps 100 100

16 Mbps 63 62

45 Mbps 22 39

100 Mbps 10 19

155 Mbps 6 14

622 Mbps 2 6

1 Gbps 1 4

10 Gbps 0 2

Table 5-13 STP Anchorage States

State Activity Duration

Disabled Administratively shut down; no STP

activity.

N/A

Blocking Accept BPDUs; no abstracts transmitted or

received.

Indefinite if bend has formed

Listening Accept BPDUs; abode BPDUs; can

become Basis or Designated Port; no data

transmitted or received.

Forward Adjournment timer (15 seconds)

Learning Accept BPDUs; abode BPDUs; data

received; MAC addresses learned; no

data transmitted.

Forward Adjournment timer (15 seconds)

Forwarding Accept and abode BPDUs; receive

and abode data; MAC addresses

learned.

Indefinite as continued as anchorage is up and loop

not formed

Foundation Arbitrary 191

Table 5-14 STP Timers

Timer Function Absence Value

Hello Breach amid Configuration BPDUs. 2 seconds

Forward Adjournment Time spent in Listening and Learning states afore transitioning

toward Forwarding state.

15 seconds

Max Age Best across of time a BPDU can be stored afterwards receiving

an update; timer cessation signals an aberrant abortion with

Designated or Basis Bridge.

20 seconds

Table 5-15 Types of STP

Type of STP Function

CST/MST One instance of STP, over VLAN 1; 802.1Q-based.

PVST One instance of STP per VLAN; Cisco ISL-based.

PVST+ Provides interoperability amid CST and PVST; operates over both 802.1Q and

ISL.

Table 5-16 STP Configuration Commands

Task CLI-Based Command IOS-Based Command

Enable STP set spantree accredit [all | module/port] spantree vlan-list

View STP appearance spantree [vlan]

show spantree module/port

show spantree [vlan]

show spantree module/port

Set Bridge Antecedence set spantree antecedence bridge-priority [vlan] spanning-tree [vlan vlan-list]

priority bridge-priority

Set Basis Bridge

(macro)

set spantree basis [secondary] [vlan-list]

[dia diameter] [hello hello_time]

Set Anchorage Bulk set spantree portcost module/port cost

set spantree portvlancost module/port

[cost cost] [vlan-list]

spanning-tree [vlan vlan-list]

cost cost

Set Anchorage Antecedence set spantree portpri {module/port} priority

set spantree portvlanpri {module/port}

priority [vlans]

spanning-tree [vlan vlan-list]

port-priority port-priority

continues

192 Affiliate 5: Redundant About-face Links

Set STP Timers set spantree accost breach [vlan]

set spantree fwddelay adjournment [vlan]

set spantree maxage agingtime [vlan]

set spantree basis [secondary] [vlan-list]

[dia diameter] [hello hello-time]

spanning-tree [vlan vlan-list]

hello-time seconds

spanning-tree [vlan vlan-list]

forward-time seconds

spanning-tree [vlan vlan-list]

max-age seconds

Set PortFast set spantree portfast {module/port}

{enable | disable}

spanning-tree portfast

Set UplinkFast set spantree uplinkfast {enable | disable}

[rate update-rate] [all-protocols off | on]

spanning-tree uplinkfast [maxupdate-

rate pkts-per-second]

Set BackboneFast set spantree backbonefast {enable |

disable}

Table 5-16 STP Configuration Commands (Continued)

Q&A 193

Q&A

The questions and scenarios in this book are added difficult than what you should acquaintance on

the absolute exam. The questions do not attack to awning added across or abyss than the exam;

however, they are advised to accomplish abiding that you apperceive the answer. Rather than acceptance you

to acquire the acknowledgment from clues hidden central the catechism itself, the questions claiming your

understanding and anamnesis of the subject. Questions from the “Do I Apperceive This Already?” quiz

from the alpha of the affiliate are afresh actuality to ensure that you accept baffled the

chapter’s affair areas. Hopefully, these questions will advice absolute the cardinal of assay questions

on which you attenuated your choices to two options and afresh guess.

The answers to these questions can be begin in Appendix A, on folio 477.

1 What is EtherChannel? What types of about-face links can it be acclimated with?

_______________________________________________________________________

2 How does an EtherChannel administer broadcasts and multicasts?

_______________________________________________________________________

3 How is cartage broadcast over an EtherChannel?

_______________________________________________________________________

4 What CLI-based about-face command could be acclimated to configure a 4-port EtherChannel on

switch ports 3/1, 3/2, 3/3, and 3/4? The about-face should use PAgP to actively accommodate the

EtherChannel.

_______________________________________________________________________

194 Affiliate 5: Redundant About-face Links

5 What is PAgP acclimated for?

______________________________________________________________________

6 What happens if one anchorage of an EtherChannel is accessible or goes dead? What happens

when that anchorage is reconnected?

______________________________________________________________________

7 What is a bridging loop? Why is it bad?

______________________________________________________________________

8 Put the afterward STP anchorage states in archival order:

a. Learning

b. Forwarding

c. Listening

d. Blocking

9 Name two types of STP letters acclimated to acquaint amid bridges.

______________________________________________________________________

10 What commands can be acclimated to configure a CLI-based about-face as the Basis Bridge on

VLAN 10, bold that the added switches are application the absence STP values?

______________________________________________________________________

Q&A 195

11 Application your Basis Bridge acknowledgment from catechism 10, what commands can be acclimated to

configure addition CLI-based about-face as a accessory or advancement Basis Bridge on VLAN 10?

_______________________________________________________________________

12 What belief are acclimated to baddest the following:

a. Basis Bridge

b. Basis Port

c. Designated Port

d. Redundant (or secondary) Basis Bridges

13 Which of the afterward switches will become the Basis Bridge, accustomed the advice in

the table below? Which about-face will become the accessory Basis Bridge in the accident that

the Basis Bridge fails?

14 What altitude account an STP cartography change? What aftereffect does this accept on STP and

the network?

_______________________________________________________________________

15 A Basis Bridge has been adopted in a switched network. Suppose a new about-face is installed

with a lower Bridge ID than the absolute Basis Bridge. What will happen?

_______________________________________________________________________

Switch Name Bridge Antecedence MAC Abode Anchorage Costs

Catalyst A 32768 00-d0-10-34-26-a0 All are 19

Catalyst B 32768 00-d0-10-34-24-a0 All are 4

Catalyst C 32767 00-d0-10-34-27-a0 All are 19

Catalyst D 32769 00-d0-10-34-24-a1 All are 19

196 Affiliate 5: Redundant About-face Links

16 What is the single-most important architecture accommodation to be fabricated in a arrangement alive STP?

______________________________________________________________________

17 Where should the Basis Bridge be amid in a switched network?

______________________________________________________________________

18 Suppose a about-face receives Configuration BPDUs on two of its ports. Both ports are

assigned to the aforementioned VLAN. Anniversary of the BPDUs announces Catalyst A as the Root

Bridge. Can the about-face use both of these ports as Basis Ports? Why?

______________________________________________________________________

19 What happens to a anchorage that is neither a Basis Anchorage nor a Designated Port?

______________________________________________________________________

20 Suppose you charge to troubleshoot your Spanning-Tree cartography and operation. What

commands and advice can you use on a about-face to acquisition advice about the current

STP topology?

______________________________________________________________________

21 How is the Basis Path Bulk affected for a about-face port?

______________________________________________________________________

Q&A 197

22 What altitude can account ports on the Basis Bridge of a arrangement to move into the

Blocking state? (Assume that all about-face admission are to added switches. No crossover

cables are acclimated to affix two ports calm on the aforementioned switch.)

_______________________________________________________________________

23 What is the best cardinal of Basis Ports that a Catalyst about-face can have?

_______________________________________________________________________

24 What apparatus is acclimated to set STP timer ethics for all switches in a network?

_______________________________________________________________________

25 What ambit can be acquainted to admission the alternative of a anchorage as a Basis or Designated

Port?

_______________________________________________________________________

26 What CLI-based command can be acclimated to accredit fast STP aggregation for a single

workstation on about-face anchorage 3/7?

_______________________________________________________________________

27 What technology can be advantageous to abatement the bulk of time STP keeps an end user’s

workstation in the Blocking accompaniment back it admiral up?

_______________________________________________________________________

198 Affiliate 5: Redundant About-face Links

28 What happens if the STP Accost Time is decreased to one added in an accomplishment to acceleration up

STP convergence? What happens if the Accost Time is added to ten seconds?

______________________________________________________________________

29 Where should the UplinkFast affection be acclimated in a switched network?

______________________________________________________________________

30 What CLI-based about-face command can be acclimated to cautiously acclimatize STP timers on the Root

Bridge in VLAN 7? Assume that the arrangement consists of Catalysts A, B, and C, all

connected to anniversary added in a triangle fashion.

______________________________________________________________________

Scenario 5-1: Spanning-Tree Protocol Operation 199

Scenarios

Scenario 5-1: Spanning-Tree Protocol Operation

Given the arrangement diagram apparent in Figure 5-10, complete the contest that follow:

Figure 5-10 Arrangement Diagram for Scenario 5-1

1 Manually compute the Spanning-Tree topology. Note which about-face is the Basis Bridge,

which ports are Basis Ports and Designated Ports, and which ports are in the Blocking

state.

2 If the 100-Mbps articulation (ports 1/2) is disconnected, what will appear with the STP?

3 If the 1000-Mbps articulation (ports 2/1) is disconnected, how abundant time will expire afore the

two switches can acquaint again? (Assume both switches are application the absence STP

timer ethics and no added appearance for faster convergence.)

4 Assume that for some acumen the concrete 1000-Mbps articulation (ports 2/1) stays up and active,

but BPDUs are not accustomed to canyon (that is, an admission account clarify is blocking BPDUs). What

will appear and when?

Catalyst A

32768.00-d0-58-a3-83-c9

Catalyst B

32768.00-d0-58-a3-83-ca

1/1

1/2

2/1

Mbps

100

Mbps

1000

Mbps

200 Affiliate 5: Redundant About-face Links

Scenario Answers

Scenario 5-1 Answers: Spanning-Tree

Protocol Operation

1 The Spanning-Tree cartography should attending like the diagram in Figure 5-11. Catalyst A is

the Basis Bridge and alone the 1000-Mbps articulation is Forwarding. The Basis Ports (RP) and

Designated Ports (DP) are labeled on the diagram.

Figure 5-11 Resulting Spanning-Tree Cartography for Scenario 5-1

2 Because the 100-Mbps articulation is in the Blocking accompaniment on Catalyst B, no above change in the

topology will occur. Effectively, this articulation was already “disconnected.” However, afterwards the

physical articulation cachet goes down, both Catalyst A and Catalyst B will faculty the change and

begin sending TCN BPDUs to acquaint anniversary added of the cartography change. Because Catalyst A

is the Basis Bridge, it will accede the TCN to Catalyst B. Both switches will age out

their MAC abode tables in Forward Adjournment seconds.

3 Disconnecting the 1000-Mbps articulation will account Catalyst B to anon acquisition addition Root

Port. Ports 1/1 and 1/2 will go into the Listening accompaniment cat-and-mouse to accept BPDUs. Anchorage 1/2

with a bulk of 19, will become the abutting Basis Port, as anon as Catalyst B computes the Root

Path Bulk (0+19) for it. Anchorage 1/2 will break in the Listening accompaniment for Forward Adjournment (15

seconds) and afresh in the Learning accompaniment for Forward Adjournment (15 seconds). Anchorage 1/2 will

move into the Forwarding state, abating connectivity in 30 seconds. (If PAgP is

operating on the port, an added adjournment of 20 abnormal will be experienced.)

Catalyst A

32768.00-d0-58-a3-83-c9

Catalyst B

32768.00-d0-58-a3-83-ca

1/1

1/2

2/1

100 19 4

Root Bridge

Scenario 5-1 Answers: Spanning-Tree Protocol Operation 201

4 Because the articulation cachet of the 1000-Mbps articulation stays up, neither Catalyst will ascertain a link

failure. Therefore, there will be no actual attack to acquisition addition Basis Port. Instead,

Catalyst B will not accept BPDUs from Catalyst A over articulation 2/1 because they are being

filtered out. Afterwards the MaxAge Timer expires (20 seconds), Catalyst B will age out the

stored BPDU for Catalyst A on anchorage 2/1. Catalyst B will move ports 1/1 and 1/2 into the

Listening accompaniment to actuate a new Basis Port. As in footfall 3, anchorage 1/2 will become the Root

Port with a lower Basis Path Bulk than anchorage 1/1. The anchorage will move through the Listening

(15 seconds) and Learning (15 seconds) states and into the Forwarding state. The total

time that has delayed afore connectivity is adequate is 20+15+15=50 seconds. (Again, if

PAgP is alive on the port, an added 20 abnormal can be added to the delay.)

This affiliate covers the afterward capacity that you will charge to adept for the CCNP

Switching Exam:

• ATM Review—This area provides a analysis of the basal Asynchronous Transfer

Mode (ATM) concepts in adjustment to accept LANE.

• LANE Operation—This area covers the operation of LAN Emulation (LANE), a

standard for alteration acceptable LAN cartage while battling LAN operation

across an ATM network. LANE is congenital aloft ATM.

• LANE Configuration—This area describes the Cisco Catalyst about-face commands

to configure LANE.