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Cisco CCNP ENCOR > Switch Trunking, STP, EtherChannel, and LAG > Flashcards

Switch Trunking, STP, EtherChannel, and LAG Flashcards

1
Q

What is VTP?

A

VLAN Trunking Protocol - not actually a trunking protocol. VTP just replicated VLAN information across switches over a trunk.

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2
Q

What is DTP?

A

Dynamic Trunking Protocol - Cisco proprietary protocol where interfaces are “desirable” or “auto” to negotiate a trunk link. This is no longer considered secure.

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3
Q

What is the IEEE standard designation for the VLAN protocol?

A

IEEE 802.1Q

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4
Q

What is the IEEE standard designation for EtherChannel aka Port-Channel?

A

IEEE 802.3AD Link Aggregation specification

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5
Q

What are the IEEE Protocol designations for Spanning Tree, Rapid Spanning Tree, and Multiple Spanning Tree?

A

Spanning Tree - 802.1d
Rapid Spanning Tree - 802.1w
Multiple Spanning Tree - 802.1s

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6
Q

What is a BPDU?

A

Bridge Protocol Data Unit - the protocol that switches use to exchange information regarding changes in topology and hierarchy.

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7
Q

What information may be found in a BPDU?

A
  • Bridge ID (BID)
  • Root Bridge ID
  • Path Cost
  • Port ID and Priority
  • TCN flag
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8
Q

What pieces of data determine a switch’s Bridge ID

A
  • Priority (default of 32,768)
  • VLAN ID (added to Priority number)
  • Base MAC Address (burned in MAC)

Example for VLAN 10: “32778 005a.ffed.0123”

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9
Q

What are the two types of BPDU?

A

Configuration BPDU - used for STP to identify root bridge, root ports, designated ports, and blocking ports.

Topology Change Notification (TCN) BPDU - used to communicate changes about the Layer 2 network topology.

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10
Q

What are the STP port costs for Ethernet, FastEthernet, GigabitEthernet, 10-Gig Ethernet, and 20-Gig Ethernet interface types?

A

Eth - 100
FastEth - 19
GigEth - 4
10Gig - 2
20Gig - 1

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11
Q

What is the Root Path Cost?

A

The STP calculated cost to reach the Root Bridge (the top switch in the STP hierarchy)

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12
Q

How is Root Path Cost Calculated?

A

The total of all egress interfaces from the local switch to the Root Bridge. (You could think of each link as of the port cost). The Root Bridge will advertise a cost of 0 to it’s directly connected neighbors.

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13
Q

How is the Root Bridge elected in an STP topology?

A

Upon coming online, all switches pass along BPDUs to their neighbors until they agree upon the switch that has the lowest Bridge ID. Lowest Priority + VLAN is best. If all priority + VLAN is the same, then the lowest base MAC address will win.

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14
Q

How is the Root Port selected?

A
  1. Lowest Port Cost
  2. Lowest upstream Lowest Bridge ID
  3. Lowest upstream port priority
  4. Lowest upstream port ID
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15
Q

In STP, what is the difference between a Designated Port and a Root Port?

A

Root port is forwarding towards the Root Bridge, Designated Port forwards away from the Root Bridge.

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16
Q

What is the maximum number of Designated Ports that can exist on one segment?

A

One. If two ports on the same link attempt to forward traffic as a designated port, they must negotiate one port as the Designated Port and the other as a Block port.

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17
Q

What determines when an STP port is “Blocked”?

A
  1. The port is not a Designated Port or a Root Port
  2. If there are two candidates for a designated port on a segment, the lowest cost port (path to root bridge) will become designated and the other will become blocked.
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18
Q

What are the six potential states of a traditional STP port?

A
  • Disabled
  • Blocking
  • Listening
  • Learning
  • Forwarding
  • Broken
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19
Q

What are the three types of an STP port?

A
  • Root Port
  • Designated Port
  • Blocking Port
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20
Q

What is RSTP?

A

Rapid Spanning Tree Protocol - an industry standard protocol that improved upon PVST and PVST+

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21
Q

What are the three port states for a RSTP port?

A
  • Discarding
  • Learning
  • Forwarding
22
Q

What are the four roles for a RSTP port?

A
  • Root Port
  • Designated Port
  • Alternate (Root) Port
  • Backup (Des) port
23
Q

What are the three port types in RSTP?

A
  • Edge port
  • Non-Edge port
  • Point-to-point port
24
Q

In traditional STP, what are the default timers for hello, max-age, and forward delay?

A

hello - 2 secs
max age - 20 secs
forward delay - 15 secs

25
Q

What does the Uplink Fast feature do?

A

It allows Spanning-Tree to transition from the Root port to the Alternate port immediately if the root port goes down. This will prevent disruption in the network in the event of a link failure.

NOTE: This feature is built into Rapid STP

26
Q

Where is the Uplink Fast feature configured?

A

Only on Access Switches

27
Q

What affect does Uplink Fast have on the port costs and bridge priority of a switch running STP?

A

Increases the bridge priority by 16,374 and increases the port costs by 3000.

28
Q

What does the Backbone Fast feature do?

A

If there is a link failure anywhere in the STP topology, it allows for fast re-convergence of the topology.

NOTE: This feature is built into Rapid STP

29
Q

Where does the Backbone fast feature need to be configured?

A

On all switches in the topology

30
Q

What does the Portfast feature do?

A

It prevents TCN BPDUs from being sent from the Switch every time an access port goes up or down. Thus, it allows clients connecting to an access port to connect more quickly.

31
Q

Where can Portfast be configured? Where should it be configured?

A

Portfast can be configured on any port, but it should be reserved for Access Ports as a general rule. Configuring Portfast on a Trunk Link can cause temporary loops.

32
Q

When Portfast is not configured and a new client is connected to an access port, what is the result to the upstream switches?

A

When they receive the TCN notification, they will remove all MAC addresses from the MAC address table that are older than 15 seconds.

33
Q

What is BDPU Filter and what does it do?

A

It prevents BPDUs from being sent unnecessarily to a client.

34
Q

What is Root Guard and what does it do?

A

Prevents a connected switch from becoming the root bridge by preventing the port from becoming a root port.

35
Q

Where would Root Guard be configured?

A

Configure on trunk ports that are connected to an access switch.

36
Q

What is BPDU Guard?

A

When portfast is enabled on a port, adding BPDU Guard will shut down the port if it sees any incoming BPDUs. This prevents loops and security-related scenarios.

37
Q

What is Loop Guard and why is it needed?

A

Loop guard prevents an alternative or backup port from taking over simply due to the loss of BPDUs being received. This can happen on unidirectional links such as Fiber Optic links where one strand could break (one stand for Tx/Rx)

38
Q

What is UDLD and why is it needed?

A

Unidirectional Link Detection is made to check fiber optic connections. It sends UDLP packets continuously back and forth to ensure the fiber link is in a good state.

39
Q

When using the show spanning-tree command. How can you tell which version of STP is running?

A

Spanning tree enabled protocol <VERSION></VERSION>

  • ieee - traditional 802.1d
  • rstp - 802.11w
  • mstp - 802.1s
40
Q

When using the show spanning-tree command. How can you tell if a port is half-duplex or full-duplex?

A

The “Type” column will reflect:
- “P2P” for Full-Duplex
- “Shr” for Hald-Duplex

41
Q

When using the show spanning-tree command. How can you tell if a neighbor is running a different version of STP?

A

The “Type” column will reflect:
- “Peer (STP)” if the switch is running 802.1w
- “Bound (PVST)” if the switch is running 802.1s

42
Q

What is the basic concept of how MST functions?

A

Instead of running a separate instance of STP for every VLAN (PVSTP), we can create a few instances of Spanning-Tree and assign VLANs to each instance.

43
Q

In MST, what is the IST?

A

Internal Spanning Tree - aka MST Instance Zero (0)

44
Q

What is unique about the way IST operates?

A

IST BPDUs will include BDPU information for all the other instances running in MST. So all the BPDUs are consolidates and distributed by the IST (Instance 0)

45
Q

When configuring MST, what three pieces of information must match on all switches to belong to the same MST Region?

A
  • MST name
  • MST revision number
  • VLAN to Instance mappings
46
Q

When using MST, what are the long value port costs for Ethernet, FastEthernet, GigabitEthernet, 10-GigEthernet, and 20-GigEthernet?

A
  • Eth - 2,000,000
  • Fast - 200,000
  • Gig - 20,000
  • 10Gig - 2,000
  • 20Gig - 1,000
47
Q

When a switch inside an MST region is communicating with a Non-MST switch, what two key things does it communicate out to the Non-MST switch?

A
  • All MST switches will tell a Non-MST switch that it’s root-path cost is “0”.
  • If the Non-MST switch is Cisco (running PVST), it will advertise the root bridge of Instance 0 as the root bridge for ALL VLANS.
48
Q

What are the two configurable port modes for PAgP (Port Aggregation Protocol?

A
  • Auto
  • Desirable
49
Q

What are the two configurable port modes for LACP?

A
  • Passive
  • Active
50
Q

Which EtherChannel protocol is Cisco proprietary and which is standard?

A

PAgP - Cisco

LACP - Industry Standard

51
Q

What are the three modes to configure a trunk port?

A
  • switchport mode trunk
  • switchport mode dynamic auto
  • switchport mode dynamic desirable

Cisco CCNP ENCOR (22 decks)

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