Ccna 3, Chapter 2

Front 1

how does mac database instability occur

Back 1

copies of the same frame are received on different ports of the switch

Front 2

what is a broadcast storm

Back 2

when there is a loop in the network, each switch may flood broadcasts endlessly

Front 3

what is multiple frame transmission

Back 3

multiple copes of unicast frames may be delivered to destination stations, can cause unrecoverable errors

Front 4

why do broadcast loops cause mac address table instability

Back 4

the mac address is constantly changing due to the same frame coming in on different ports.

Front 5

when does a broadcast storm occur

Back 5

when there are so many broadcast frames caught in a layer 2 loop that all available bandwidth is consumed.

Front 6

spanning tree protocol function

Back 6

ensures that there is only one logical path between all destinations on the network

Front 7

how does spanning tree protocol work

Back 7

logically blocks redundant paths that can cause a loop

Front 8

a port is considered to be blocked when

Back 8

user data is prevented from entering or leaving that port

Front 9

BPDU stands for

Back 9

bridge protocol data unit

Front 10

what happens when a cable or switch failure occurs in an stp enabled network

Back 10

stp recalculates the paths and unblocks the necessary ports to allow the redundant path to become active

Front 11

RSTP stands for

Back 11

rapid spanning tree protocol

Front 12

MSTP stands for

Back 12

multiple spanning tree protocol

Front 13

IEEE documentation on spanning tree

Back 13

IEEE 802.1D

Front 14

STA stands for

Back 14

spanning tree algorithm

Front 15

how does the sta determine the root bridge

Back 15

all switches participating exchange bpdu frames to determine which switch has the lowest bid

Front 16

BID stands for

Back 16

bridge id

Front 17

What is a BPDU

Back 17

a messaging frame exchanged by switches for STP

Front 18

what does the BPDU contain that helps with STP

Back 18

a BID containing a priority value and the MAC address of the sending switch

Front 19

What happens after the root bridge has been determined

Back 19

the STA calculates the shortest path to the root bridge.

Front 20

what does the STA consider while making its calculation

Back 20

path and port costs

Front 21

how are path costs calculated

Back 21

using port cost values associated with port speeds for each switch port along a given path. sum of those determines overall path cost to root bridge.

Front 22

4 roles that can be assigned to a port by the STA

Back 22

root port

designated port

alternate/backup port

disabled port

Front 23

root port is

Back 23

switch ports closest to the root bridge on each switch

Front 24

designated port is

Back 24

all non-root ports that are still permitted to forward traffic

Front 25

other end of a root port is a

Back 25

designated port

Front 26

alternate/backup ports are

Back 26

configured to be in a blocked state to prevent loops. only on trunk links where neither end is a root port. only one end is blocked

Front 27

disabled port is

Back 27

one that is shut down

Front 28

frequency of sending out BPDU frames

Back 28

every 2 seconds

Front 29

default port costs defined by

Back 29

speed at which the port operates

Front 30

new cost of 10 Gb/s port

Back 30

1

Front 31

cost of 1 Gb/s port

Back 31

1

Front 32

cost of 100 Mb/s port

Back 32

10

Front 33

cost of 10 Mb/s port

Back 33

100

Front 34

spanning tree cost command

Back 34

S2(config-if)# spanning-tree cost __

Front 35

why would you want to configure a new spanning tree cost on an interface

Back 35

to manually control the spanning tree paths to the root bridge

Front 36

old cost of 10 Gb/s port

Back 36

2

Front 37

old cost of 1 Gb/s port

Back 37

4

Front 38

old cost of 100 Mb/s port

Back 38

19

Front 39

old cost of 10MGb/s port

Back 39

100

Front 40

command to verify port and path cost to the root bridge

Back 40

S1# show spanning-tree

Front 41

ports in the root bridge are automatically configured as

Back 41

designated

Front 42

if all port costs are equal, how are designated and alternate switch ports determined

Back 42

through the BPDU process, the switch with the lower BID has the designated ports

Front 43

how is the root port determined on each switch

Back 43

the switch port with the lowest overall path cost to the root bridge

Front 44

number of root ports on each switch

Back 44

one

Front 45

number of fields in the BPDU frame

Back 45

12

Front 46

1st 4 fields of a BPDU frame

Back 46

protocol

version

message type

status flag

Front 47

2nd 4 fields of BPDU frame

Back 47

root id

cost of path

bridge id

port id

Front 48

3rd 4 fields of BPDU frame

Back 48

message age

max age

hello time

forward delay

Front 49

multicast mac address for spanning tree group

Back 49

01:80:C2:00:00:00

Front 50

if the priority on all switches are the same, how is the root bridge determined

Back 50

lowest MAC address

Front 51

when identifying a root bridge, what part of the BPDU does not get updated

Back 51

Bridge ID for each switch

Front 52

customizable part of the BID field

Back 52

bridge priority

Front 53

default bridge priority for Cisco switches

Back 53

32768

Front 54

range and increments of bridge priority for Cisco switches

Back 54

0 to 61440, increments of 4096

Front 55

value to set bridge priority to make sure it is the root bridge

Back 55

0

Front 56

what information is in the extended switch id portion of the BID

Back 56

VLAN id

Front 57

if 2 switches have the same priority and extended switch id, how is the lowest BID determined

Back 57

the lowest MAC address

Front 58

6 varieties of spanning tree protocols

Back 58

802.1D-1998

PVST+

802.1D-2004

RSTP

Rapid PVST+

Multiple Spanning Tree Protocol

Front 59

RSTP stands for

Back 59

rapid spanning tree protocol

Front 60

802.1D-1998 is

Back 60

the legacy standard for bridging and STP

Front 61

CST stands for

Back 61

common spanning tree

Front 62

CST assumes

Back 62

one spanning tree instance for the entire bridged network regardless of number of vlans

Front 63

PVST+ is

Back 63

Cisco's enhancement of STP that provides separate spanning trees for each VLAN

Front 64

802.1D-2004 is

Back 64

and updated version of the STP standard incorporating IEEE 802.1W

Front 65

RSTP is, AKA

Back 65

evolution of STP that provides faster convergence than STP, AKA IEEE 802.1W

Front 66

Rapid PVST+ is

Back 66

Cisco enhancement that provides a separate instance of 802.1w per VLAN

Front 67

MISTP stands for

Back 67

multiple instance STP

Front 68

MSTP stands for

Back 68

multiple spanning tree protocol

Front 69

what does MSTP do

Back 69

maps multiple vlans into the same spanning tree instance, up to 16 of RSTP

Front 70

STP protocol standard resources needed, convergence, tree calculation

Back 70

802.1D

Low

Slow

All VLANs

Front 71

PVST+ protocol standard resources needed, convergence, tree calculation

Back 71

Cisco

High

Slow Per VLAN

Front 72

RSTP protocol standard resources needed, convergence, tree calculation

Back 72

802.1w

Medium

Fast

All VLANs

Front 73

Rapid PVST+ protocol standard resources needed, convergence, tree calculation

Back 73

Cisco

Very High

Fast

Per VLAN

Front 74

MSTP protocol standard resources needed, convergence, tree calculation

Back 74

802.1s, Cisco

Medium or high

Fast

Per instance

Front 75

why are cpu and memory requirements low for IEEE 802.1D

Back 75

only one instance of spanning tree, only one root bridge,

Front 76

PVST+ allows for

Back 76

per VLAN root bridges, optimizing traffic of each VLAN

Front 77

One thing RSTP and STP have in common

Back 77

only provides a single instance of STP

Front 78

Difference between RSTP and Rapid PVST+

Back 78

supports separate instance of 802.1w per VLAN

Front 79

default spanning tree mode for Cisco switches

Back 79

PVST+

Front 80

cisco enhancement of STP, provides a separate 802.1D spanning tree instance for each VLAN

Back 80

PVST+

Front 81

Cisco enhancement of RSTP

Back 81

Rapid PVST+

Front 82

Uses one IEEE 802.1D spanning tree instance for entire bridged network

Back 82

STP

Front 83

An evolution of STP that provides faster STP convergence

Back 83

RSTP

Front 84

Maps multiple VLANs that have the same traffic flow requirements into the same spanning tree instance

Back 84

MSTP

Front 85

2 characteristics of a network running CST

Back 85

No load sharing possible

the CPU is spared, only 1 instance of spanning tree must be computed

Front 86

Advantages of PVST+ over CST

Back 86

Supports spanning tree for each VLAN so can block for 1 vlan while allowing traffic for another on the same trunk

can implement layer 2 load balancing

Front 87

disadvantages of PVST+

Back 87

requires greater CPU process and BPDU bandwidth consumption than CST

Front 88

2 characteristics of network running PVST+

Back 88

Optimum load balancing capabilities

Can have waste of CPU cycles due to each VLAN having own spanning tree

Front 89

5 port states that ensure no loops are created during creation of spanning tree

Back 89

blocking

listening

learning

forwarding

disabled

Front 90

blocking states means

Back 90

port is an alternate port and does not participate in frame forwarding

Front 91

listening state means

Back 91

listens for the path to the root. can receive, transmit BPDU frames and inform adjacent switches that the port is preparing to participate in active topology

Front 92

learning state means

Back 92

learns MAC addresses to participate in frame forwarding, begins to populate the MAC address table

Front 93

forwarding state means

Back 93

forwards data frames and sends/receives
BPDU frames. Active

Front 94

disabled state means

Back 94

does not participate in spanning tree and does not forward frames. Amin disabled

Front 95

4 steps PVST+ performs to provide loop free network topology

Back 95

Elects one root bridge

selects the root port on each non-root bridge

selects the designated port on each segment

remaining ports in the switches network are alternate ports

Front 96

RSTP port states

Back 96

discarding

learning

forwarding

Front 97

version field of BPDU for RSTP

Back 97

2

Front 98

Difference in use of BPDU in RSTP

Back 98

BPDU used as a keep-alive, 3 consecutively missed BPDUs indicate lost connectivity

Front 99

an RSTP edge port is

Back 99

a switch port that is never intended to be connected to another switch, immediately transitions to the forwarding state when enabled

Front 100

command to configure edge ports

Back 100

S1(config-if)# spanning-tree portfast

Front 101

2 different link types

Back 101

point to point

shared

Front 102

point to point link type is

Back 102

a port operating in full duplex mode typically connects a switch to a switch and is a candidate for a rapid transition to a forwarding state

Front 103

shared link type is

Back 103

a port operating in half duplex mode connects a switch to a hub that attaches multiple devices

Front 104

type of port that most uses link type parameters

Back 104

designated

Front 105

Uses 802.1D to run a separate instance for each vlan

Back 105

PVST+

Front 106

Possible to have load sharing with some vlans forwarding on each trunk

Back 106

PVST+ and Rapid PVST+

Front 107

CPU processing and trunk bandwidth usage is greater than with STP

Back 107

PVST+ and Rapid PVST+

Front 108

The root bridge is determined by the lowest BID+VLAN ID + MAC

Back 108

PVST+ and Rapid PVST+

Front 109

Cisco proprietary protocol

Back 109

PVST+ and Rapid PVST+

Front 110

Ports can transition to forwarding state without relying on a timer

Back 110

Rapid PVST+

Front 111

Port roles, root, designated, alternate, edge, backup

Back 111

Rapid PVST+

Front 112

Sends a BPDU hello message every 2 seconds

Back 112

PVST+ and Rapid PVST+

Front 113

Cisco 2960 default enable state

Back 113

Vlan 1

Front 114

Cisco 2960 default spanning tree mode

Back 114

PVST+

Front 115

Cisco 2960 default switch priority

Back 115

32768

Front 116

Cisco 2960 default spanning tree priority

Back 116

128

Front 117

Cisco 2960 default spanning tree port cost

Back 117

1000 Mb/s: 4

100 Mb/s: 19

10 Mb/s: 100

Front 118

Cisco 2960 default spanning tree vlan port priority

Back 118

128

Front 119

Cisco 2960 default spanning tree vlan port cost

Back 119

1000 Mb/s: 4

100 Mb/s: 19

10 Mb/s: 100

Front 120

spanning tree hello time

Back 120

2 seconds

Front 121

spanning tree forward-delay time

Back 121

15 seconds

Front 122

spanning tree max aging time

Back 122

20 seconds

Front 123

spanning tree transmit hold count

Back 123

6 BPDU

Front 124

command to ensure a switch has the lowest bridge priority value (vlan)

Back 124

s1(config)#spanning-tree vlan __ root primary

Front 125

What does the spanning-tree vlan ___ root primary do

Back 125

sets the priority for the switch to the predefined value of 24,576 or to the highest multiple of 4096, less than the lowest bridge priority detected on the network

Front 126

command to set an alternate root bridge

Back 126

s2(config)# spanning-tree vlan ___ root secondary

Front 127

what does the alternate root bridge command do

Back 127

sets the priority for the switch to 28,672

Front 128

command to exactly configure bridge priority value

Back 128

s1(config)# spanning-tree vlan __ priority ___

Front 129

what does portfast do

Back 129

enables a port to transition from blocking to forwarding state immediately by passing the listening and learning states

Front 130

Portfast is a feature for which spanning tree protocol?

Back 130

PVST+

Front 131

Where is portfast usually used

Back 131

on access ports connected to end devices

Front 132

What does BPDU guard do

Back 132

puts the port into error disabled state if it receives a BPDU

Front 133

why is Portfast useful for DHCP

Back 133

without it, it's possible for an end device to request an IP address before the port is active

Front 134

command to configure portfast

Back 134

s1(config-if)# spanning-tree portfast

Front 135

what does the command spanning-tree portfast default do

Back 135

enables Portfast on all nontrunking interfaces

Front 136

command to configure BPDU guard on a port

Back 136

s2(config-if)# spanning-tree bpduguard enable

Front 137

show command to check that BPDU guard has been enabled

Back 137

show running-config

Front 138

command to display active interface spanning tree config

Back 138

show spanning-tree active

Front 139

when is a spanning tree instance created

Back 139

when an interface is assigned to a vlan

Front 140

command to configure rapid PVST+

Back 140

S1(config)# spanning-tree mode rapid-pvst

Front 141

command to get a quick overview of the status of STP for all vlans that are defined on a switch

Back 141

show spanning-tree

Front 142

command to get STP info for a particular vlan

Back 142

show spanning-tree vlan ___

Front 143

2 types of STP failures

Back 143

STP might erroneously block ports that should have gone into the forwarding state

STP erroneously moves one or more ports into the forwarding state

Front 144

Earliest indication of a broadcast storm

Back 144

routers or layer 3 switches report control plane failures and high cpu loads

Front 145

ways to prevent a single point of failure at the default gateway

Back 145

virtual router

Front 146

what is a virtual router

Back 146

multiple routers configured to work together to present the illusion of a single router to the hosts on a LAN

Front 147

what do routers share when they are a virtual router

Back 147

a MAC and IP address

Front 148

how does a virtual router route packets

Back 148

virtual router IP configured as default

host uses ARP to resolve MAC address of default gateway

frames sent to virtual router MAC address are processed by the current active router

Front 149

first-hop redundancy is

Back 149

the ability of a network to dynamically recover from the failure of a device acting as a default gateway

Front 150

a device that routes traffic destined to network segments beyond the source network segment for which the sending node may not have explicit routing information

Back 150

default gateway

Front 151

a set of routers working together to present the illusion of a single router to the hosts on a LAN segment

Back 151

virtual router

Front 152

a layer 3 address assigned to a protocol that shares the single address among multiple devices

Back 152

virtual ip address

Front 153

a device that is part of a virtual router group assigned the role of alternate default gateway

Back 153

standby router

Front 154

the layer 2 address returned by arp for an fhrp gateway

Back 154

virtual mac address

Front 155

a device that is part of a virtual router group assigned to the role of default gateway

Back 155

forwarding router

Front 156

command to verify HSRP state

Back 156

show standby

Front 157

HSRP stands for

Back 157

hot standby router protocol

Front 158

What is HSRP

Back 158

Cisco-proprietary FHRP designed to allow for transparent failover of a first-hop ipv4 device.

Front 159

Where is HSRP used

Back 159

in a group of routers for selecting an active device and standby device

Front 160

function of HSRP

Back 160

monitor the operational status of the HSRP group and quickly assume packet forwarding responsibility if active router fails

Front 161

HSRP ipv6 virtual mac address is derived from

Back 161

the HSRP group number

Front 162

HSRP ipv6 virtual IPv6 link-local address is derived from

Back 162

HSRP virtual MAC address

Front 163

VRRPv2 stands for

Back 163

Virtual router redundancy protocol version 2

Front 164

What is VRRPv2

Back 164

non-proprietary election protocol that dynamically assigns responsibility for one or more virtual routers to the VRRP routers

Front 165

VRRPv2 supports

Back 165

IPv4 only

Front 166

VRRPv2 supports

Back 166

IPv4 and IPv6

Front 167

GLBP stands for

Back 167

gateway load balancing protocol

Front 168

Function of GLBP

Back 168

FHRP that protects data traffic from a failed router or circuity while also allowing load balancing

Front 169

IRDP stands for

Back 169

ICMP router discovery protocol

Front 170

what is IRDP

Back 170

a legacy FHRP solution

Front 171

Cisco proprietary FHRP protocol which protects data traffic from a failed router or circuit while also allowing load sharing between a group of redundant routers

Back 171

GLBP

Front 172

Used in a group of routers for selecting an active device and a standby device

Back 172

HSRP

Front 173

Cisco proprietary FHRP protocol designed to allow for transparent failover of a first hop IPv4 device

Back 173

HSRP

Front 174

One router is elected as the virtual router master, with the other routers acting as backups in case the virtual router master fails

Back 174

VRRP

Front 175

A non-proprietary election protocol that allows several routers on a multi-access link to utilize the same virtual IPv4 address

Back 175

VRRP

Front 176

4 characteristics of an HSRP active router

Back 176

responds to default gateway's ARP request

Assumes active forwarding of packets

sends hello messages

knows the virtual router IP address

Front 177

2 characteristics of a HSRP standby router

Back 177

listens for periodic hello packets

assumes active forwarding of packets if it does not hear from the active router

Front 178

Advantages of GLBP

Back 178

since it allows for load balancing between non-active routers it utilizes some of the bandwidth that would otherwise be dormant

Front 179

4 characteristics of GLBP

Back 179

Allows full use of resources on all devices without admin

provides single virtual IP and MAC address

routes traffic to a single gateway distributed across routers

provides automatic rerouting in the event of any failure

Front 180

command to verify GLBP status

Back 180

show glbp