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Network CCNP > Spanning Tree > Flashcards

Spanning Tree Flashcards

1
Q

How is the root bridge elected in STP?

A

Lowest bridge ID. Bridge ID is made up of lowest priority and MAC address.

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2
Q

What are the 3 port types of STP?

A

Designated Port = FWD Root Port = FWD Non Designated (Alternate) Port = Blocking

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3
Q

What ports are found on a root bridge?

A

All ports on the Root Bridge are Designated Ports

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4
Q

What ports are closest (facing) the Root Bridge?

A

Root Ports

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5
Q

What determines the closest path to a Root Bridge?

A

COST of the links it take to get back to the Root. 1G=4 100M = 19 10M= 100

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6
Q

What is the special frame used to negotiate STP?

A

BPDU (Bridge Protocol Data Unit)

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7
Q

What is the default STP Priority?

A

32768

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8
Q

What are the 4 STP Modes?

A

Blocking Listening Learning Forwarding

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9
Q

How long do each of the modes take?

A

Blocking 20 Sec Listening 15 Sec Learning 15 Sec Forwarding

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10
Q

What is happening during the listening mode?

A

The switch will only be sending and receiving BPDU’s

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11
Q

What is happening during the learning mode?

A

The switch will only be sending and receiving BPDU’s along with learning MAC address. No data transmission until in forward mode.

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12
Q

What are default Hello Times for STP?

A

2 seconds

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13
Q

What is the default Max age timers for STP?

A

20 Seconds

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14
Q

What is CST & PVST+ Reconvergence time?

A

50 Seconds Total

  • 20 Sec Max Age Timer
  • 15 Sec Listening
  • 15 Sec Learning
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15
Q

What is the default STP mode for cisco switches?

A

PVST

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16
Q

What does PortFast do.

A

It skips the Listening and Learning stage of STP.

A port with Portfast will never create a topology change noticication (TCN).

17
Q

When STP has to make a decesion, what 4 tie breakers will it use?

A

1. Lowest bridge ID: the switch with the lowest bridge ID becomes the root bridge.

2. Lowest path cost to root bridge: when the switch receives multiple BPDUs it will select the interface that has the lowest cost to reach the root bridge as the root port.

3. Lowest sender bridge ID: when a switch is connected to two switches that it can use to reach the root bridge and the cost to reach the root bridge is the same, it will select the interface connecting to the switch with the lowest bridge ID as the root port.

4. Lowest sender port ID: when the switch has two interfaces connecting to the same switch, and the cost to reach the root bridge is the same it will use the interface with the lowest number as the root port.

18
Q

What is RSTP and PVRSTP average converge times?

A

2-3 seconds.

19
Q

How do you enable PortFast?

A

under the interface

#spanning-tree portfast

or

Global#spanning-tree portfast Default (enable portfast on all access mode interfaces)

20
Q

What are the steps of RSTP?

A

1, Discarding

  1. Learning
  2. Forwarding
21
Q

Who send BPDU after the network has been converged in CST?

A

The root bridge generates BPDU’s and they are relayed by none root bridges.

22
Q

Who generates BPDU’s in RSTP?

A

All Switches generate BPDU every two seconds (Hello Time)

23
Q

How are BPDU’s used as keepalive mechanism in RSTP?

A

If a switch misses 3 BPDU from a neighbor it will assume connectivity to ths switch has been lost and it will remove all MAC address.

24
Q

Name the two types of BPDU’s?

A

Type 1 : configuration BPDU

Type 2: TCN BPDU

25
Q

How do you set a root bridge for a VLAN?

A

SW2(config)#spanning-tree vlan 20 root Primary

26
Q

What is uplink Fast?

A

a Manual setting on CST that puts all ports that connect back to RB in a group. The blocking port is in standby. When the Root Port fails the standby port goes straight into forwarding state.

27
Q

Where would you use uplink fast?

A

Only use uplink fast in the access layer of the network. Uplink fast set switch priority to 49,152 so it does not become root.

28
Q

What is backbone fast?

A

Backbone fast will null the max age timer on a blocking interface. A switch should only receive a Root BPDU on a blocking interface if the connected switch looses connection to the Root Bridge.

29
Q

What is BPDU Guard?

A

Blockes all BPDU’s from entering a port. If BPDU are received then the port will go into err-disabled.

30
Q

How to enable BPDU guard?

A

SW1(config-if)#spanning-tree bpduguard enable

Or

SW1(config)#spanning-tree portfast bpduguard default (enable on all ports with portfast enabled)

31
Q

What port types does RSTP have?

A

Edge ports & P2P ports.

32
Q

What are the 5 versions of Spanning Tree?

A
  • Common Spanning Tree 802.1D
  • PVLAN+ (Cisco Only)
  • RSTP 802.1W
  • PVRST (Cisco Only)
  • MST 802.1S

Network CCNP (7 decks)

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