Title: ICND2 / 1. LAN Switching Technologies

Q: 802.1D refers to what protocol?
A: Spanning-tree Protocol

Q: Switches send “probes” into the network called _____ in order to discover loops.  If a switch sends out a ____ on port fa0/1, and receives that same ____ on port fa0/2, a loop has been discovered.
A: BPDUs

Q: BPDUs also help elect the core switch of the network, called the _________
A: ROOT BRIDGE

Q: BPDUs are composed of the [_____________&_____________], these two things combined are called the “Bridge ID”
A: Bridge Priority,
Switch MAC Address

Q: How often are BPDUs sent?
A: The default is once every 2 seconds. Thy are sent from thr root bridge down

Q: What is the default bridge ID?
A: 32768 (65536/2)

Q: The Root Bridge is the switch with the ______ Bridge ID.
A: LOWEST

Q: The Root Bridge has ALL _________ ports
A: Designated

Q: What is the STP Cost for a 10Mbps link?
A: 100

Q: What is the STP Cost for a 100Mbps link?
A: 19

Q: What is the STP Cost for a 1Gbps link?
A: 4

Q: What is the STP Cost for a 10Gbps link?
A: 2

Q: What is the order of steps STP takes to determine the best path to the root bridge?
A: Find the lowest cost link
Find the switch with the lowest bridge ID
Find the lowest port number
(Enable 1 designated port per link)
(Block everything else)

Q: What is a Bridge ID comprised of?
A: Bridge Priority and MAC Address

Q: 802.1W refers to what protocol?
A: Rapid Spanning Tree Protocol

Q: What are the three port states in 802.1w (RSTP)
A: Discarding
Learning
Forwarding

Q: In regards to RSTP:
The root port and designated port roles from STP remain, while the blocking port role is split into the _________ and _________ port roles.
A: backup, alternate

Q: In regards to RSTP:
The Spanning Tree Algorithm (STA) determines the role of a port based on _______.
A: Bridge Protocol Data Units (BPDUs).

Q: The port that receives the best BPDU on a bridge is the _________.
A: root port

Q: A(n) __________  port receives more useful BPDUs from another bridge and is a port blocked.
A: alternate

Q: A(n) __________ port receives more useful BPDUs from the same bridge it is on and is a port blocked.
A: backup

Q: In regards to RSTP:
A port on a switch that connects to a client machine is considered a(n) ______________.
A: Edge Port

Q: (802.1w;RSTP)The ___________ concept is already well known to Cisco spanning tree users, as it basically corresponds to the PortFast feature.
A: Edge Port

Q: What happens when an Edge Port receives a BPDU?
A: It immediately loses its Edge Port status and becomes a normal spanning tree port.

Q: When using the "show interfaces fa0/1 status" command, is it possible to see whether or not a port is being blocked by spanning-tree?
A: No, this command will not note the stp port state.

Q: How often does a nonroot bridge or switch send an 802.1D
STP hello BPDU message?
A: Nonroot switches forward hellos received from the root; the root sends these hellos based on the root’s configured hello timer. (default=every 2 seconds)

Q: Assuming VLANs are in use and the switch is connected to another switch via a trunk, what will happen if the switch receives a frame with a MAC address that is not in the switches CAM table?
A: The switch will flood the frame out all other access ports in that same VLAN and out all trunk ports that list this VLAN as fully supported (active, in the allowed list, not pruned, STP forwarding)

Q: What three problems can be caused by not using spanning-tree?
A: Broadcast storms
MAC address table instability
Multiple frame transmission

Q: Can a switchport in STP blocking state still learn MAC addresses?
A: No. Interfaces that block do not forward user frames, do not learn MAC addresses of received frames, and do not process received user frames.

Q: In regards to STP, what is the default value for the Hello timer?
A: 2 seconds

Q: In regards to STP, what is the default value for the MaxAge timer?
A: Hello timer x10

Q: In regards to STP, what is the default value for the Forward delay timer?
A: 15 seconds

Q: What happens if a switch does not receive any BPDUs for the time of the set Hello timer?
A: The switch continues as normal until the time of Hello x10 passes.

Q: What happens if a switch does not receive any Hellos on an interface for Hello x10 seconds?
A: The switch will renegotiate a root bridge and make all of its STP choices all over again.

Q: What happens during the Listening state in STP?
A: The switch removes MAC entries from its MAC table for interfaces it doesn't receive traffic on while it's in this state.

Q: STP moves an interface from blocking to listening, then to learning, and then to forwarding state. STP leaves the interface in each interim state for a time equal to the _______________ timer, which defaults to 15 seconds.
A: forward delay

Q: Can EtherChannel provide a way to prevent spanning-tree protocol from converging?
A: Yes. EtherChannel combines multiple parallel segments of equal speed (up to eight) between the same pair of switches, bundled into an EtherChannel. The switches treat the EtherChannel as a single interface with regard to STP. As a result, if one of the links fails, but at least one of the links is up, STP convergence does not have to occur.

Q: How do you set the spanning-tree priority on a switch for a specific VLAN?
A: SW2(config)#spanning-tree vlan 1 priority 4096

Q: What command would you issue to make the switch set it's priority to whatever it needs to be to become the root bridge for a specific VLAN?
A: SW1(config)#spanning-tree vlan 1 root primary

Q: What command would you issue to make the switch set it's priority to whatever it needs to be to become the backup root bridge for vlan 1?
A: spanning-tree vlan 1 root secondary

Q: In the following output, what does the "sys-id-ext 1" mean?
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     0001.4389.8910
             Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  20
A: This is showing the spanning-tree information for VLAN1

Q: What command would you use to create an EtherChannel?
A: Switch(config-if)#channel-group <#> mode on

Q: What command would you use to see any configured EtherChannels?
A: Switch#show etherchannel

Q: What two commands would you use to see the root cost of a switch?
A: SW1#show spanning-tree
SW1#show spanning-tree root

Q: Name a Cisco-proprietary improvement of 802.1D STP.
A: Per VLAN Spanning-Tree+ (PVST+ or PVSTP)

Q: Which protocol introduced PortFast?
A: PVST+

Q: What is the Cisco improvement of RSTP 802.1W?
A: Rapid Per VLAN Spanning-tree Protocol Plus (RPVST+)

Q: When dealing with PVSTP+, what values are you allowed to use for the priority?
A: Multiples of 4096 up to 61440.

Q: With PVSTP+, why are you allowed to only use multiples of 4096 up to 61440 for the priority?
A: Because the priority is only a 4 bit field, with a maximum of 16 total values.

Q: Label the three areas of the PVSTP+ Bridge ID:
A: 1. Bridge Priority
2. System ID Extension (VLAN ID, 1-4094, requires 12 bits)
3. System ID (MAC Address, requires 6 bytes)

Q: When using PVSTP+, why is the bridge ID often listed as 32769?
A: Because the default priority is 32768 and the VLAN is 1, so the Bridge ID ends up 32769

Q: With PVST+, you can view the 16-bit priority as a _________ plus the _________.
A: base priority,
VLAN ID

Q: How would you configure a STP switch port's cost for a specific VLAN?
A: SW1(config-if)#spanning-tree VLAN 1 cost x

Q: What happens if you use the "spanning-tree cost X" command without specifying a VLAN?
A: The spanning-tree cost will be set to X for all VLANs that haven't had their cost manually configured.

Q: How would you enable BPDU guard?
A: spanning-tree bpduguard enable

Q: How would you enable PortFast
A: SWITCH1(config-if)#spanning-tree portfast default

Q: What command could you issue to see the local switches Bridge ID information?
A: SW1#show spanning-tree bridge

Q: By default, portfast and bpduguard are disabled on all interfaces.  How would you reverse this default and enable these interfaces on all interfaces?
A: SW1(config)#spanning-tree portfast default
SW1(config)#spanning-tree portfast bpduguard default

Q: If you have enabled portfast and bpduguard on all switch interfaces, how would you quickly disable it?
A: SW1(config)#spanning-tree portfast disable
SW1(config)#spanning-tree bpduguard disable

Q: After creating channel-group/EtherChannel, how would you see the interface number?
A: Switch#show etherchannel summary
Flags:  D - down        P - in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port
Number of channel-groups in use: 1
Number of aggregators:           1
Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------
1      Po1(SU)           -      Fa0/1(P) Fa0/2(P) Fa0/3(P) Fa0/4(P) Fa0/5(P) Fa0/6(P) Fa0/7(P) Fa0/8(P)

Q: What does 802.3ad refer to?
A: Link aggregation (port trunking/combining multiple network connections in parallel in order to increase throughput)

Q: What does LACP stand for?
A: Link Aggregation Control Protocol

Q: (802.3ad)Desirable and auto keywords enable ____, while active and passive keywords enable LACP.
A: PAgP (Port aggregation Protocol)

Q: In reference to EtherChannels, are you allowed to use 'on' on one end of the link but use "auto" or "desirable" on the other?  For example:
SWITCH1(config-if)#channel-group 1 mode on
SWITCH2(config-if)#channel-group 1 mode auto
A: No.  Do not use the 'on' parameter on one end, and either auto or desirable (or for LACP, active or passive) on the neighboring switch. The on option uses neither PAgP nor LACP, so a configuration that uses on, with PAgP or LACP options on the other end, would prevent the EtherChannel from working.

Q: Is it possible for a switch that has a root port to be the Root Bridge?
A: No.  Root Bridges have all designated ports.

Q: What are two commands you could use to find out a switches root port?
A: SWITCH1#show spanning-tree
SWITCH1#show spanning-tree root

Q: When a switch is trying to choose a root port and there are two interfaces with a tie, what happens?
A: It will chose the switch with the lowest Bridge ID.

Q: When taking the ICND2 exam, is it okay to assume that default costs are being used when calculating spanning-tree?
A: No.  Do not assume default costs are being used.

Q: What are the RSTP port states?
A: Discarding
Learning
Forwarding

Q: What is the significance of the forward delay timer?
A: It specifies how long to keep ports in the listening and learning states when transitioning from blocking to forwarding.  (Default time of 15 seconds)

Q: When configuring EtherChannel, can the channel-group number be different on the local switch?
A: No, all interfaces in the same EtherChannel must have the same number.

Q: When configuring EtherChannel, can the channel-group number be different on the neighboring switch?
A: Yes, the channel-group number can be different on the neighboring switches.

Q: When configuring EtherChannel, can you use "mode on" on the local switch, and "mode desirable" on the neighboring switch?
A: No, you must use "mode on" on the corresponding interfaces of both switches

Q: When configuring EtherChanel, if you use the desirable keyword on one switch, the switch uses PAgP; therefor the other switch must use either ________ or ____.
A: desirable, auto

Q: When configuring EtherChannel, if you use the active keyword on one switch, the switch uses LACP; the other switch must use either ______ or _______.
A: active, passive

Q: For interfaces to be able to work together in the EtherChannel properly, what must be the same on all of the interfaces?
A: • Speed
• Duplex
• Operational access or trunking state (all must be access, or all must be trunks)
• If an access port, the access VLAN
• If a trunk port, the allowed VLAN list (per the switchport trunk allowed command)
• If a trunk port, the native VLAN
• STP interface settings

Q: When configuring EtherChannel, if the ports are trunk ports, but have different allowed VLANS will the channel-group be successful?
A: No, the allowed VLAN list must be the same for all interfaces.

Q: When configuring EtherChannel, if the interfaces in the channel-group are all trunks but one has a different native vlan, will it function with the group?
A: No.  All trunks must have the same VLANs allowed as well as the same native VLAN to function in an EtherChannel together.

Q: When configuring EtherChannel, do all of the interfaces in the channel-group need to have the same STP settings?
A: Yes.

Q: When configuring EtherChannel, if interfaces have different STP costs, will the EtherChannel be able to form?
A: No, all interfaces must have the same cost.

Q: How do you recover physical and PortChannel interfaces from ErrDisable state?
A: From the PortChannel interface, do:
shutdown --> no shutdown

Q: How would you set which version of spanning-tree you're running?
A: SWITCH1(Config)#spanning-tree mode pvst|rapid-pvst|mst

Q: How would you change the spanning tree priority for a given interface on a given vlan?
A: SWITCH1(config-if)#spanning-tree vlan 1 port-priority (0-240, increments of 16)

Q: How would you change PortFast on all interfaces from disabled to enabled?
A: SWITCH1(config)#spanning-tree portfast default

Q: How would you disable portfast on a single interface?
A: SWITCH1(config-if)#spanning-tree portfast disable

Q: How would you disable bpduguard on a single interface?
A: SWITCH1(config-if)#spanning-tree bpduguard disable

Q: Passive and Active are modes from _____________. (EtherChannel technology)
A: LACP (Link Aggregation Control Protocol)

Q: Auto and Desirable are modes from _____________. (EtherChannel technology)
A: PAgP (Port Aggregation Protocol)

Q: VLAN ___ is used for the management of VLANs. It is the VLAN used for protocols such as Cisco Discovery Protocol (CDP) for example.
A: 1

Q: Can VLAN 1 traffic be pruned?
A: VLAN 1 traffic cannot be pruned. VTP pruning is a Cisco VTP feature that allows switches to dynamically delete or add VLANs to a trunk for traffic transmission. It creates an efficient switching network by optimal use of available trunk bandwidth. However, management traffic on VLAN 1 cannot be pruned, as it is important for efficient network operation.

Q: When using port-security and setting the violation mode, do you set this globally or per interface?
A: Per interface.

Q: How would you see which version of spanning-tree you're running for a specific VLAN?
A: SW1#show spanning-tree vlan 1
VLAN0001
  Spanning tree enabled protocol rstp <----------------------------------------
  Root ID    Priority    32769
             Address     000f.34b0.ba80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000f.34b0.ba80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time  300 sec
Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/1               Desg BLK 19        128.1    P2p

Q: Do 802.1q trunks require matching native VLANs at both ends?
A: Yes.

Q: If spanning tree is blocking interfaces that are configured as a trunk, what color will the led be?  How about if the interfaces are configured as access ports?
A: blocked trunks = green,
blocked access ports = amber

Q: What does LAG stand for?
A: Link Aggregation.

Q: Which one EtherChannel protocol is Cisco proprietary?
A: PAgP

Q: Which Etherchannel is industry standard?
A: LACP

Q: What does "on" in the following command do?:
SW1(config-if)#channel-group 1 mode on
A: Specifies a default etherchannel bundle.  Not PAgP nor LACP.

Q: (Etherchannel)Why shouldn't you use the "on" keyword when configuring etherchannel? (channel-group 1 mode on)
A: Because if one side is "on" and the other side is misconfigured, there is no way to tell that it is misconfigured and it will drop all packets.

Q: When using etherchannel, should you do it in groups of odds or evens?
A: You should do it in groups of evens, the hardware/algorithm is geared to perform on even groups of interfaces.

Q: (Etherchannel Protocols)
_____: Desirable, Auto
_____: Active, Passive
A: PAgP: Desireable, Auto
LACP: Active, Passive

Q: What Etherchannel setup modes are recommended by Cisco?
A: Either of the following:
Desirable paried with Auto
Active paired with Passive
Desirable+Desirable and Active+Active will work, however.

Q: (Etherchannel)Base interfaces must have identical:
1. _________
2. _________
3. _________
4. _________
A: 1. Speed
2. Duplex
3. Mode
4. VLANs

Q: After you configure your etherchannel, where is all future configure done?
A: On the virtual port-channel interface

Q: Why don't etherchannels inherit speed and duplex along with allowed VLANs and mode?
A: Because speed and duplex are physical configurations (as opposed to logical).

Q: How would you remove a single VLAN from being allowed over a trunk port?
A: SW3(config-if)#switchport trunk allowed vlan remove #

Q: Which is used to view the VTP statistics information?
A: Router#show vtp counters
VTP statistics:
Summary advertisements received: 7
Subset advertisements received: 6
Request advertisements received: 0
Summary advertisements transmitted: 894
Subset advertisements transmitted: 13
Request advertisements transmitted: 3
Number of config revision errors: 0
Number of config digest errors: 0
Number of V1 summary errors: 0
VTP pruning statistics:
Trunk Join Transmitted Join Received Summary advts received
from on-pruning-capable device
---------------- ---------------- ---------------- --------------------
Fa0/2 43450 42691 6