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CCNA > STP > Flashcards

STP Flashcards

1
Q

What is the IEEE standard for:
STP
PVSTP
RSTP

A

802.1D
Cisco Proprietary
802.1w

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2
Q

What does RSTP stand for?

A

Rapid Spanning Tree Protocol

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3
Q

What STP mode do Cisco switches generally default to?

A

802.1D with PVST

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4
Q

Command to set a switch to use PVST

A

spanning-tree mode pvst

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5
Q

What 3 fields make up the BID?

A
  1. Priority
  2. System ID Extension
  3. System ID
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6
Q

What is the range for priority?

A

0-65535

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7
Q

What is unusual about the priority value?

A

It’s in multiples of 4096.

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8
Q

What is the value of an all 1’s priority field?

A

61140

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9
Q

What are the values of each bit in the priority field?

A

32768 16384 8192 4096

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10
Q

What is normally stored in the System ID extension field?

A

VLAN ID

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11
Q

How many bits in the System ID extension field?

A

12

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12
Q

How many bits in the priority field?

A

4

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13
Q

How many bits in the System ID field?

A

6 bytes

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14
Q

What’s in the System ID field?

A

The BIA of the switch

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15
Q

Is the System ID configurable?

A

No, that’s supplied automatically by the switch.

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16
Q

What is the decimal value of the first 2 bytes of the BID if the priority field is 0010 and the vlan is 12?

A

8204

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17
Q

Command to set the priority for a given VLAN

A

spanning-tree vlan vlan id priority priority

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18
Q

Command to set a port cost.

A

Conf t
interface gi1/0
spanning-tree [vlan vlan id] cost cost

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19
Q

What is the default BID priority?

A

32768

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20
Q

Is portfast or bpduguard enabled by default?

A

No

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21
Q

What are the 3 port types in STP?

A
  1. Root port
  2. Designated port
  3. Blocking port
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22
Q

What is a Designated port vs other port types?

A

It’s a port that is not the closest to the root switch (root port), but is still forwarding and not blocking (blocking port). This is also related to the fact that this port is where the root switch’s BPDU will be forwarded out of.

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23
Q

What state are all the ports on the root switch in?

A

They are all forwarding.

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24
Q

What types of ports (in STP language) does the root switch have: root, designated, blocking, disabled.

A

Designated

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25
Q

What 4 fields are shown in a “show mac address-table” output?

A
  1. VLAN
  2. MAC address
  3. Type (dynamic or static)
  4. Output port to get to that MAC
26
Q

What does “show interfaces status” show us (7 fields)?

A
  1. Port
  2. Description
  3. Status (connect / notconnect/ disabled)
  4. VLAN
  5. Duplex
  6. Speed
  7. Type (10/100/1000 TX etc)
27
Q

If a frame came into a switch and was either an unknown destination MAC or a broadcast mac, what ports would the switch forward it out of?

A

All forwarding ports for that VLAN, except the one on which it was received.

28
Q

What makes a switch a designated switch for a given ethernet segment?

A

It’s the switch (and therefor the port) that is forwarding the root’s BPDU.

29
Q

4 important fields in a Hello BPDU

A
  1. Root BID
  2. Sender’s BID
  3. Sender’s root cost
  4. Timers on the root switch
30
Q

What are 3 of the timers on the root switch?

A
  1. Hello timer
  2. MaxAge timer
  3. Forward Delay timer
31
Q

What is the most common type of BPDU?

A

Hello BPDU

32
Q

What does STA stand for?

A

Spanning Tree Algorithm

33
Q

What is the root cost in a BPDU received directly from the root bridge?

A
  1. The root bridge has a 0 cost to reach itself.
34
Q

If a switch receives a BPDU with a root cost of 25 on a 1 gig port with default costing, what will it rewrite the root cost to be?

A

29

25 + 4 for the gig port

35
Q

Which switch’s BID would win?
A: 32769:0200.0002.0002
B: 32769:0200.0003.0003

A

A, since it has the numerically lower System ID

36
Q

If a switch is connected to a hub and hear’s it’s own BPDU’s on multiple ports, what are the other 2 tiebreaker values?

A
  1. Lowest interface STP priority

2. If all interfaces are the same priority, lowest interface number.

37
Q

What 2 items will a non-root switch change before forwarding out the hello BPDU received from the root’s direction?

A
  1. Root cost

2. Sender ID

38
Q

What is the default value of the 3 primary STP timers?

A
  1. Hello - 2 seconds
  2. MaxAge - 20 seconds
  3. Forward Delay - 15 seconds
39
Q

What is the calculation to get the MaxAge time?

A

MaxAge = 10*(Hello timer)

40
Q

What does the forward delay timer control?

A

How long a port will transition through Listening and Learning before going to Forwarding. Each phase will take (fwddelay value) seconds.

41
Q

What does the MaxAge timer control?

A

How long a switch will wait for a Hello BPDU before declaring the neighbor down and sending out a TCN BPDU.

42
Q

How many interfaces can be included in an Etherchannel?

A

Up to 8.

43
Q

What does PortFast do?

A

Allows a port to go immediately into Forwarding, without the normal interim stages of Listening and Learning.

44
Q

What kinds of ports must PortFast be restricted to?

A

Access ports facing stubs only, never anything that could be cabled up to form a loop.

45
Q

What does BPDUguard do?

A

When a port has it configured, it will immediately become disabled if a BPDU is received on that port.

46
Q

In RSTP, what is the blocking state called?

A

Discarding

47
Q

What is STP’s convergence time vs RSTP?

A

STP - 50 seconds

RSTP - max 10 seconds, usually much less

48
Q

What does the command “spanning-tree vlan vlan-id root {primary | secondary}” do?

A

The switch on which this is configured will lower it’s own priority to beat out any other switch to become the root bridge.

49
Q

Command to enable portfast on gi1/0.

A

conf t
int gi1/0
spanning-tree portfast

50
Q

Command to enable BPDUguard on gi1/0

A

conf t
int gi1/0
spanning-tree bpduguard enable

51
Q

Command to make a switch root or secondary root.

A

spanning-tree vlan vlan-id root {primary | secondary}

52
Q

Command to see the root BID.

A

show spanning-tree [vlan vlan id]

53
Q

Command to list the root switches for all vlans.

A

show spanning-tree root

54
Q

Command to show the BID broken out into it’s component parts.

A

show spanning-tree vlan vlan id bridge

55
Q

Command to debug STP

A

debug spanning-tree events

56
Q

When using the root primary command, what is the value that the switch’s priority will be set to if the current root is at 32768?

A

24576

57
Q

When using the root primary command, what is the value that the switch’s priority will be set to if the current root is less than 24576?

A

The highest multiple of 4096 that is still less than the priority of the current root.

58
Q

What are the 3 port states of 802.1w?

A
  1. Learning
  2. Forwarding
  3. Discarding
59
Q

2 commands to see if a switch is in PVST or RPVST mode

A

show spanning-tree

show spanning-tree summary

60
Q

Command to set either PVST or RPVST

A

conf t

spanning-tree mode [pvst | rapid-pvst]

61
Q

If a switch has a root port, is it the root switch?

A

No. The root switch only has designated ports.

62
Q

How many root ports will a switch have?

A

1 per vlan

CCNA (11 decks)

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