Vol 1 Ch 10 RSTP and EtherChannel Configuration

Question 1

What is the size of the priority field used for RSTP and RSTP+?

Answer 1

The field size is 16 bits long, the first four bits are for the priority number, which is a multiple of 4,096, and the last 12 bits is for the VLAN ID. For RTSP, the VLAN ID is all zeroes because RSTP does not create STP per VLAN. For RSTP+, the VLAN ID is used fro the VLAN ID, with values from 1 to 4095.

Question 2

What is the adjoining the priority field in RSPT?

Answer 2

Next to the 16-bit priority field composed of 4 bits for priority number at 12 bits for VLAN ID, there is the 48 bit System ID - MAC address field.

Question 3

What are some configurable priority values for RSTP?

Answer 3

The priority values are all multiples of 4096.
0
4096
...
28672
32768

Question 4

How is the final priority value calculated?

Answer 4

The final priority value is calculated by the switch as a sum of the configurable priority value (first 4 bits) and the VLAN ID 9last 12 bits).

Example;
Priority 32777 (priority 32768 sys-id-ext 9)

Question 5

Which of the two SPT standards (RSTP or RSTP+) works with VLANs?

Answer 5

Standard RSTP behaves as if VLANs do not exits, while Cisco’s RSTP+ integrates VLAN information into the entire process.

Question 6

If there is no EtherChannel, what would happen to multiple links between two switches?

Answer 6

With no EtherChannel, all links would be blocked except for one., due to RSTP that is turned on by default on Cisco switches.

Question 7

Is RSTP turned on by fault on Cisco switches?

Answer 7

Yes.

Question 8

On which layers can EtherChannel be implemented?

Answer 8

EtherChannel can be implemented in one of two ways, as layer 2 or layer 3.

Question 9

What are the two DYNAMIC configuration options for configuring EtherChannel?

Answer 9

The two DYNAMIC configuration options for EtherChannel are:

1. Cisco-proprietary Port Aggregation Protocol (PAgP)
2. IEEE standard Link Aggregation Control Protocol (LACP

Question 10

What are the three synonymous terms when configuring EtherChannel?

Answer 10

EtherChannel
PortChannel
Channel-group

Question 11

How are interfaces added to an EtherChannel?

Answer 11

The interfaces must be added via the interface command mode.

In the example below, I am adding two interfaces to channel-group “1”. Note that mode must be “on”

enable
conf t
interface fa0/14
channel-group 1 mode on
interface fa 0/15
channel-group 1 mode on
^Z

Question 12

What two show commands can I use to check EtherChannel?

Answer 12

1. show spanning-tree vlan ___

2. show etherchannel ___ summary

Question 13

How do I configure PAgP?

Answer 13

Interface range fa 0/3 -4
channel-group 2 mode desirable
exit

Note: at least one end of the link must be in mode DESIRABLE. The other end can be in mode DESIRABLE or AUTO.

Question 14

How do I configure LACP?

Answer 14

interface ranfe fa 0/3 - 4
channel group 3 mode active
exit

Note: at least one end of the link must be in mode ACTIVE. The other end can be in mode ACTIVE or PASSIVE.

Question 15

What command do I use to configure load distribution on an EtherChannel?

Answer 15

port-channel load-balance ______

The default is src-mac

Options include:
src-mac
dst-mac
src-dst-mac
src-ip
dst-ip
src-dst-ip
src-port
dst-port
src-dst-port

Question 16

What global configuration command do I use to set-up the spanning-tree mode?

Answer 16

spanning-tree mode [pvst | rapid-pvst | mst]

Question 17

what global configuration command do I use to make a switch “root primary”

Answer 17

spanning-tree [vlan ______] root primary

NOTE: This command sets the priority to the lower of 24,676 or 4,096 less of the curent root bridge.

Question 18

what global configuration command do I use to make a switch “root secondary”

Answer 18

spanning-tree [vlan ______] root secondary

NOTE: This command sets the priority to 28,672.

Question 19

List of GLOBAL commands for SPT

p 259

Answer 19

spanning-tree mode [pst | rapid-pvst | mst]

spanning-tree [vlan ________] root primary

spanning-tree [vlan ________] root secondary

spanning-tree vlan ______ priority _______

Question 20

List of INTERFACE commands for SPT

p 259

Answer 20

spanning-tree [vlan ________] cost _______

spanning-tree [vlan _________] port-priority _______