As a frame leaves a Layer 3 device, the Layer 2 encapsulation information is changed from what it was when it entered the device. For what two reasons can this happen?()A. The data is moving from 10BASE-TX to 100BASE-TX.B. The WAN encapsulation type has c

Transport layer divides a data stream into segments & adds reliability & flow control information

Data link layer adds physical source & destination address & an FCS to the segment

Packets are created when the network layer encapsulate a frame with source & destination host address& protocol related control information

Packets are created when the network layers adds layers 3 address & control information to a segment

The presentation layer translated bits into bits into voltages for transmission across the physical link

to verify the type of cable interconnecting two devices

to determine the status of network services on a remote device

to obtain VLAN information from directly connected switches

to verify Layer 2 connectivity between two devices when Layer 3 fails

to obtain the IP address of a connected device in order to telnet to the device

to determine the status of the routing protocols between directly connected routers

The access layer is the initial point at which traffic enters the network. Traffic is marked （orremarked） at Layers 2 and 3 by the access switch as it enters the network， or is trusted that it isentering the network with the appropriate tag

No traffic marking occurs at the core layer. Layer 2/3 QoS tags are trusted from distributionlayer switches and used to prioritize and queue the traffic as it traverses the core

Traffic inbound from the access layer to the distribution layer can be trusted or reset dependingupon the ability of the access layer switches. Priority access into the core is provided based onLayer 3 QoS tags

IP precedence， DSCP， QoS group， IP address， and ingress interface are Layer 2 characteristics that are set by the access layer as it passes traffic to the distribution layer. Thedistribution layer， once it has made a switching decision to the core layer， strips these off

MAC address， Multiprotocol Label Switching （MPLS）； the ATM cell loss priority （CLP） bit， theFrame Relay discard eligible （DE） bit， and ingress interface are established by the voicesubmodule （distribution layer） as traffic passes to the core layer

The distribution layer inspects a frame to see if it has exceeded a predefined rate of trafficwithin a certain time frame， which is typically a fixed number internal to the switch. If a frame isdetermined to be in excess of the predefined rate limit， the CoS value can be marked up in a waythat results in the packet being dropped

to uniquely identify devices at Layer 2

to allow communication with devices on a different network

to differentiate a Layer 2 frame from a Layer 3 packet

to establish a priority system to determine which device gets to transmit first

to allow communication between different devices on the same network

to allow detection of a remote device when its physical address is unknown

bridging VLANs on two switches

bridging two VLANs on one switch

between two Layer 2 devices withtrunking

between two Layer 2 devices withouttrunking

between a Layer 2 device and a Layer 3 device withtrunking

The data is moving from 10BASE-TX to 100BASE-TX.

The WAN encapsulation type has changed.

The data format has changed from analog to digital.

The source and destination hosts are in the same subnet.

The source and destination MAC addresses have changed.

When an OTV edge device receives a Layer 2 frame destined for a remote data center site， the frame is logically forwarded to the overlay interface.

The OTV edge device performs the dynamic OTV encapsulation on the Layer 2 packet and sends it to the join interface toward the routed domain.

When the OTV edge device receives a Layer 2 frame destined for a remote data center site， the frame is logically forwarded to the join interface.

The OTV edge device performs the dynamic OTV encapsulation on the Layer 2 packet and sends it to the overlay interface toward the routed domain.

VLAN support

compression

authentication

sliding windows

multilink support

quality of service

end-to-end communications path

hosts on the same Layer 2 broadcast domain

hosts on the same Layer 3 broadcast domain

routing information on participating Layer 3 devices

The data is moving from 10BASE-TX to 100BASE-TX.

The WAN encapsulation type has changed.

The data format has changed from analog to digital.

The source and destination hosts are in the same subnet.

The source and destination MAC addresses have changed.

The transport layer divides a data stream into segments and may add reliability and flow control information.

The data link layer adds physical source and destination addresses and an FCS to the segment.

Packets are created when the network layer encapsulates a frame with source and destination host addresses and protocol-related control information.

Packets are created when the network layer adds Layer 3 addresses and control information to a segment.

The presentation layer translates bits into voltages for transmission across the physical link.

bridging VLANs on two switches

bridging two VLANs on one switch

between two Layer 2 devices with trunking

between two Layer 2 devices without trunking

between a Layer 2 device and a Layer 3 device with trunking

to verify the type of cable interconnecting two devices

to determine the status of network services on a remote device

to obtain VLAN information from directly connected switches

to verify Layer 2 connectivity between two devices when Layer 3 fails

to obtain the IP address of a connected device in order to telnet to the device

to determine the status of the routing protocols between directly connected routers