STP/EtherChannel

Question 1

What is portfast?

How do you enable it?

Answer 1

If portfast is enabled on a port, it transitions to forwarding immediately, effectively disabling spanning tree for that port.

(if)spanning-tree portfast

Question 2

What is BPDU-guard?

How do you enable it?

Answer 2

BPDU guard automatically disables a port if a BPDU is received on it, preventing loops when portfast is enabled.

(if)spanning-tree bpduguard enable

Question 3

How do you make portfast/BPDU-guard the default port state?

Answer 3

()spanning-tree portfast bpduguard default

Question 4

What is root guard?

How do you enable it?

Answer 4

It prevents the root bridge from being changed by disabling a port if it receives a BPDU from a higher priority bridge than it’s own root bridge on that port.

(if)spanning-tree guard root

Question 5

How do you manually set the primary and secondary root bridge?

Answer 5

()spanning-tree vlan 1 root primary

()spanning-tree vlan 1 root secondary

Question 6

What command allows you to see the STP configuration a Cisco switch?

Answer 6

show spanning-tree vlan 1

Question 7

Why do you need to specify the vlan when checking STP configuration on Cisco switches?

Answer 7

PVST+ is the default STP, and it has a separate spanning tree instance for each vlan.

Question 8

What is “alternate port”?

Answer 8

Alternate port means blocking role in PVST+

Question 9

Unlike dynamic routing protocols, STP cannot do what for subnets?

Answer 9

STP does not load balance across equal cost paths like dynamic routing protocols do, it just chooses whichever has lowest bridge ID.

Question 10

What PVST+ command always ensure a switch is the root for a particular VLAN?

Answer 10

()spanning-tree vlan 750 priority 0

Question 11

How do you make a switch the root bridge for VLAN without changing priority?
What should be noted about this command?

Answer 11

()spanning-tree vlan 750 root primary

Switches made the primary with this will be overridden by a switch manually configured with priority 0

Question 12

What value can you modify to configure a specific port as the preferred forwarding/designated port?

Answer 12

port priority

Question 13

What are major uses of CDP?

Answer 13

finding the interface IPs of neighboring devices.

verifying L2 connectivity if L3 connectivity goes down.

finding the power requirement of a connected Cisco PD on a PoE switch.

IOS version running

host name

duplex settings

Question 14

CDP can communicate what info about VTP and VLANs?

Answer 14

It can only communicate the VTP domain

It can only communicate the native VLAN, no other VLAN information is given.

Question 15

Which is Cisco proprietary, PAgP or LACP?

What states do they have?

Answer 15

PAgP; desirable/auto. Cisco

LACP; passive/active. Open.

Question 16

What are PAgP and LACP configured with?

Answer 16

Both use the channel-group command:

(if) # channel-group 1 mode active
(if) # channel-group 1 mode desirable

Question 17

What is static etherchannel configured with?

Answer 17

(if)# channel-group 1 mode on

Question 18

What is notable about static etherchannel?

Answer 18

It is not compatible with LACP and PAgP enabled ports.

Question 19

difference between LLDP holdtime and reinit time?

Answer 19

holdtime - how long device will hold onto information before discarding it (default 120)

-reinit - delay time in seconds for LLDP to initialize on an interface (default 2)

Question 20

What happens when an adjacent CDP device is configured without an IP address?

Answer 20

it uses another interface’s IP address for that neighbor