quiz2

Bridge Priority:

The default priority value for all Cisco switches is the decimal value 32768

Extended System ID

The extended system ID value is a decimal value added to the bridge priority value in the BID to identify the VLAN for this BPDU.

What additional information is contained in the 12-bit extended system ID of a BPDU?

Vlan ID

after the election fo the root bridge has been completed, how will switches find the best paths to the root bridge?

each switch will analyze the sum of all port costs to reach the root and use the path with the lowest cost.

Currently each EtherChannel can consist of up to

eight compatibly-configured Ethernet ports

All switches in the broadcast domain participate in the

election process.

how often are bpdu's are sent?

every 2 seconds

*if you have a layer 2 loops, a switch is unable to

forward frames

Which port state will switch ports immediately transition to when configured for PortFast?=

forwarding

The path information, known as the internal root path cost

is determined by the sum of all the individual port costs along the path from the switch to the root bridge.

*LACP

link aggregation control protocol

ether channel automatically configures

load balancing

root port determined by

lowest cost to root bridge

*MSTP

maps mutiple vlan's into the same spanning tree instance

*EtherChannel does what?

multiple physical Ethernet links together into one single logical link, It provides fault-tolerance, *load sharing*, *increased bandwidth*, and redundancy between switches, routers, and servers.

can you ether port a gig and a ethernet connection togeather?

no, they must be the same

The show etherchannel summary command displays

one line of information per port channel.

SU on show ethersummary

port is down

SD on show ethersummary

port not established

The Bridge ID contains a

priority value, the MAC address of the switch, and an extended system ID (vlan ID).The lowest BID value is determined by the combination of these three fields.

*PVST+ standard

provides a separate 802.1D spanning tree instance for each VLAN

STP compensates for a failure in the network by

recalculating and opening up previously blocked ports.

STP stops

redundent paths/loops

The STA designates a single switch as the root bridge and uses it as the

reference point for all path calculations.

BPDUs are used to elect the

root bridge, root ports, designated ports, and alternate ports.

*RSTP port rolls

root port Designated port Backup port, alternate port

Switches exchange BPDUs to

select the root bridge.

*STP

spanning tree protocol, layer 2 loop prevention protocol

inconsistant mac talbe if

stp is not turned on to prevent flood of frames

An EtherChannel link can only be created between

switches

Which two statements describe a switch port that is configured with PortFast?

switchport immediately transitions from blocking to forwarding state, or listening to forwarding state

When two switches are configured with the same priority and have the same extended system ID, how do the switches determine bridge priority

the MAC address with the lowest value, expressed in hexadecimal, will have the lower BID.

bridge id values determine which switch will be

the root bridge

if they all match the switch with the lowest mac address is

the root bridge

*In EtherChannel, it is mandatory that all ports have

the same speed, duplex setting, and VLAN information. Any port modification after the creation of the channel also changes all other channel ports.

how do routers stop loops

time to live

Switches do not have TTL

time to live, unlike routers they cannot discard data

portfast eliminates the time wasted on

trying to descover the DHCP server

what is the port roll of back up ports on RSTP port rolls?

used for hubs

*MST

wich provides up to 16 instances of RSTP

PAgP modes

On, PAgP desirable, PAgP auto

*only 2 protocols usable on ether channel

PAGP, and LACP

default protocol spanning tree is

PVST+

cisco ios runs what protocols for STP

PVST+ and RSTP

*PAGP

Port Aggregation Protocol, cisco only version

BID of the root bridge, known as the

Root ID.

*STP port rols

Root port, designated port, blocked port

If a switch port transitions directly from the blocking state to the forwarding state without information about the full topology during the transition, the port can temporarily create a data loop. For this reason,

STP has five ports states, four of which are operational port states blocking, listening, learning, forwarding. The disabled state is considered non-operational

difference between listening state and learning state

both recieve and send data, learning updates mac table, listening does not, the both do not forward frame data

When the root bridge has been elected for a given spanning tree instance, the STA starts determining the best paths to the root bridge from all destinations in the

broadcast domain

*layr 2 loop

broadcast storm

Without STP enabled, Layer 2 loops can form, causing?

broadcast, multicast and unknown unicast frames to loop endlessly. This can bring down a network quickly.

STP is enabled when?

by default to prevent broadcast storms

The individual EtherChannel group member port configuration must be

consistent on both devices.

If one end of a segment is a root port, the other end is a

designated port.

All ports on the root bridge are

designated ports.

*STP port states

disable, blocking, listening, learning, forwarding

The switches running STP are able to compensate for failures by ?

dynamically unblocking the previously blocked ports and permitting traffic to traverse the alternate paths.

STP prevents loops from occurring by configuring a loop-free path through the network using strategically placed what?

"blocking-state" ports.

range of bridge priority

0 - 61440

PAgP packets are sent every

30 seconds

*how long from blocking state to forwarding state on a port?

30 seconds, from listening forwarding delay (15sec) to learning forward delay (15sec)

Lowest Sender Port Priority

This topology has two switches which are connected with two equal-cost paths between them. S1 is the root bridge, so both of its ports are designated ports

a bridge priority can be changed in incriments of

4096

EtherChannel

A link aggregation technology is needed that allows redundant links between devices that will not be blocked by STP

on access ports, you have 2 options for port status

BPDU and port-fast

During STA and STP functions, switches use (BPDUs)

Bridge Protocol Data Units to share information about themselves and their connections.

*RSTP port stats

Discarding, learning, forwarding

why is a port configured alternate and block

blocked logically, if other path fails the blocked port opens up

Using the STA, STP builds a loop-free topology in a four-step process

Elect the root bridge., Elect the root ports., Elect designated ports., Elect alternate (blocked) ports.

*STP standard is

IEE 802.1D

*RSTP standard

IEE802.1W

by default, a port can only be in 2 states

blocking and forwarding

A Layer 2 loop can result in

MAC address table instability, link saturation, and high CPU utilization on switches and end-devices, resulting in the network becoming unusable.

When a switch port is configured with PortFast, that port transitions from

blocking to forwarding state immediately

PAgP auto

This PAgP mode places an interface in a passive negotiating state in which the interface responds to the PAgP packets that it receives but does not initiate PAgP negotiation.

PAgP desirable

This PAgP mode places an interface in an active negotiating state in which the interface initiates negotiations with other interfaces by sending PAgP packets.

Selecting a Root Bridge

This bridge (switch) is the reference point for the entire network to build a spanning tree around.

PAgP on

This mode forces the interface to channel without PAgP. Interfaces configured in the on mode do not exchange PAgP packets.

*port channel

When an EtherChannel is configured, a port channel is created from the bundled physical interfaces.

port fast shoud only be enabled on what type of port?

access ports