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Exam Automating Cisco Service Provider Solutions (300-535 SPAUTO)
Number 300-535
File Name Cisco.300-535.ExamLabs.2020-01-09.26q.vcex
Size 822 KB
Posted Jan 09, 2020
Download Cisco.300-535.ExamLabs.2020-01-09.26q.vcex

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Demo Questions

Question 1

On a Cisco IOS XR router, which mechanism protects the router resources by filtering and policing the packets flows that are destined to the router that is based on defined flow-type rates?


  1. LLQ
  2. LPTS
  3. Committed Access Rate
  4. Control Plane Policing
  5. Management Plane Protection
  6. NetFlow
  7. ACL
Correct answer: B
Explanation:
Local Packet Transport Services (LPTS) maintains tables describing all packet flows destined for the secure domain router (SDR), making sure that packets are delivered to their intended destinations. The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).
Local Packet Transport Services (LPTS) maintains tables describing all packet flows destined for the secure domain router (SDR), making sure that packets are delivered to their intended destinations. 
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).



Question 2

When configuring LLQ (strict priority queue) on a traffic class using the Cisco IOS XR priority command on a Cisco ASR9K router, which additional QoS command is required for this traffic class?


  1. shape
  2. police
  3. random-detect
  4. bandwidth
Correct answer: B
Explanation:
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).



Question 3

When implementing MPLS DS-TE on Cisco IOS XR routers, all aggregate Cisco MPLS TE traffic is mapped to which class type by default?


  1. class-type 0 (bandwidth global pool)
  2. class-type 1 (bandwidth subpool)
  3. class-type 2 (bandwidth priority)
  4. class type class-default (bandwidth best-effort)
Correct answer: A
Explanation:
Differentiated Services Traffic Engineering MPLS Differentiated Services (Diff-Serv) Aware Traffic Engineering (DS-TE) is an extension of the regular MPLS-TE feature. Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. To support various classes of service (CoS), users can configure multiple bandwidth constraints. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint. MPLS diff-serv traffic engineering provides the ability to configure multiple bandwidth constraints on an MPLSenabled interface. Available bandwidths from all configured bandwidth constraints are advertised using IGP. TE tunnel is configured with bandwidth value and class-type requirements. Path calculation and admission control take the bandwidth and class-type into consideration. RSVP is used to signal the TE tunnel with bandwidth and class-type requirements. Diff-Serv TE can be deployed with either Russian Doll Model (RDM) or Maximum Allocation Model (MAM) for bandwidth calculations.  TE Class Mapping Each of the eight available bandwidth values advertised in the IGP corresponds to a TE Class. Because the IGP advertises only eight bandwidth values, there can be a maximum of only eight TE classes supported in an IETF DS-TE network. TE class mapping must be exactly the same on all routers in a DS-TE domain. It is the responsibility of the operator configure these settings properly as there is no way to automatically check or enforce consistency. The operator must configure TE tunnel class types and priority levels to form a valid TE class. When the TE class map configuration is changed, tunnels already up are brought down. Tunnels in the down state, can be set up if a valid TE class map is found. Table 4 TE Classes and Priority     The default mapping includes four classes types.
Differentiated Services Traffic Engineering 
MPLS Differentiated Services (Diff-Serv) Aware Traffic Engineering (DS-TE) is an extension of the regular MPLS-TE feature. Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. To support various classes of service (CoS), users can configure multiple bandwidth constraints. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint. 
MPLS diff-serv traffic engineering provides the ability to configure multiple bandwidth constraints on an MPLSenabled interface. Available bandwidths from all configured bandwidth constraints are advertised using IGP. 
TE tunnel is configured with bandwidth value and class-type requirements. Path calculation and admission control take the bandwidth and class-type into consideration. RSVP is used to signal the TE tunnel with bandwidth and class-type requirements. 
Diff-Serv TE can be deployed with either Russian Doll Model (RDM) or Maximum Allocation Model (MAM) for bandwidth calculations. 
TE Class Mapping 
Each of the eight available bandwidth values advertised in the IGP corresponds to a TE Class. Because the IGP advertises only eight bandwidth values, there can be a maximum of only eight TE classes supported in an IETF DS-TE network. 
TE class mapping must be exactly the same on all routers in a DS-TE domain. It is the responsibility of the operator configure these settings properly as there is no way to automatically check or enforce consistency. 
The operator must configure TE tunnel class types and priority levels to form a valid TE class. When the TE class map configuration is changed, tunnels already up are brought down. Tunnels in the down state, can be set up if a valid TE class map is found. 
Table 4 TE Classes and Priority 
  
The default mapping includes four classes types.



Question 4

On the Cisco IOS XR, which MQC configuration is different than on the Cisco IOS and IOS XE?


  1. On the Cisco IOS XR, WRED can only be applied in the output direction.
  2. On the Cisco IOS XR, marking can only be applied in the input direction.
  3. On the Cisco IOS XR, LLQ can be applied in the input or output direction.
  4. On the Cisco IOS XR, LLQ can use up to four priority queues: level 1, level 2, level 3, and level 4.
Correct answer: C



Question 5

Refer to the Cisco IOS XR policy-map configuration exhibit. 
  
What is wrong with the policy-map configuration?


  1. missing the priority percent command under class one and class two
  2. missing the police command under class one and class two
  3. missing the police command under class three
  4. missing the priority bandwidth command under class one and class two
  5. missing the bandwidth command under class one and class two
Correct answer: B
Explanation:
Hierarchical policing is also supported. In such a configuration, both parent and child policies have class-maps containing policing statements, as in the following example:! policy-map child class gold police rate percent 50 conform-action set precedence immediate exceed-action drop ! ! policy-map parent class match_all police rate 10000 kbps burst 15000 exceed-action drop service-policy child
Hierarchical policing is also supported. In such a configuration, both parent and child policies have class-maps 
containing policing statements, as in the following example:
policy-map child 
class gold 
police rate percent 50 conform-action set precedence immediate exceed-action 
drop 
policy-map parent 
class match_all 
police rate 10000 kbps burst 15000 exceed-action drop 
service-policy child



Question 6

When configuring class-based WRED on Cisco routers, which WRED parameter is not user configurable on a Cisco IOS XR but is user configurable on a Cisco IOS and IOS XE?


  1. the ingress or egress direction where the class-based WRED policy will be applied
  2. the maximum threshold
  3. the minimum threshold
  4. the mark probability denominator
Correct answer: D
Explanation:
Comparison of Cisco IOS QoS and Cisco IOS-XR QoS The Cisco IOS-XR software implementation of QoS is basically the same as the QoS implementation on Cisco IOS software, with the following exceptions:On Cisco IOS-XR software, the bandwidth command can be configured only in egress policies. The following changes have been made to the class-map command on Cisco IOS-XR software:Supports 4K per logical router. Maximum number of match criteria configurable in one class map is eight. When a class is marked as high priority using the priority command on Cisco IOS-XR software, we recommend that you configure a policer to limit the priority traffic. Limiting the priority traffic will ensure that the priority traffic does not starve all of the other traffic on the line card. Use the police command to explicitly configure the policer. On Cisco IO-XR software, only one conform-action, exceed-action, or violate-action command can be configured at a time. To configure traffic policing, use the police command. On Cisco IOS-XR software, policy modifications cannot be made on existing policies. Use the policy-map command to remove the policy from all attached interfaces, delete the policy map, and redefine a new policy. When configuring a policy map on Cisco IOS-XR software, the maximum number of classes configurable in one policy map is 16, which includes both Level 1 and Level 2 classes. To configure a policy map, use the policy-map command. When WRED is configured on Cisco IOS-XR software, the mark probability in the random-detect command is not configurable—it is always set to 1. When the random-detect exp command is used on Cisco IOS-XR software, the exponential weighting constant is not configurable and will be programmed automatically by Cisco IOS-XR software. When access control lists (ACLs) are used in QoS class maps, the underlying deny or permit actions associated with access control entries (ACEs) are ignored. ACEs are used as a classification mechanism in order to provide appropriate QoS behavior as specified in class maps. Use ACLs that include ACEs with permit actions only.
Comparison of Cisco IOS QoS and Cisco IOS-XR QoS 
The Cisco IOS-XR software implementation of QoS is basically the same as the QoS implementation on Cisco 
IOS software, with the following exceptions:
  • On Cisco IOS-XR software, the bandwidth command can be configured only in egress policies. 
  • The following changes have been made to the class-map command on Cisco IOS-XR software:
    • Supports 4K per logical router. 
    • Maximum number of match criteria configurable in one class map is eight. 
  • When a class is marked as high priority using the priority command on Cisco IOS-XR software, we recommend that you configure a policer to limit the priority traffic. Limiting the priority traffic will ensure that the priority traffic does not starve all of the other traffic on the line card. Use the police command to explicitly configure the policer. 
  • On Cisco IO-XR software, only one conform-action, exceed-action, or violate-action command can be configured at a time. To configure traffic policing, use the police command. 
  • On Cisco IOS-XR software, policy modifications cannot be made on existing policies. Use the policy-map command to remove the policy from all attached interfaces, delete the policy map, and redefine a new policy. 
  • When configuring a policy map on Cisco IOS-XR software, the maximum number of classes configurable in one policy map is 16, which includes both Level 1 and Level 2 classes. To configure a policy map, use the policy-map command. 
  • When WRED is configured on Cisco IOS-XR software, the mark probability in the random-detect command is not configurable—it is always set to 1. 
  • When the random-detect exp command is used on Cisco IOS-XR software, the exponential weighting constant is not configurable and will be programmed automatically by Cisco IOS-XR software. 
  • When access control lists (ACLs) are used in QoS class maps, the underlying deny or permit actions associated with access control entries (ACEs) are ignored. ACEs are used as a classification mechanism in order to provide appropriate QoS behavior as specified in class maps. Use ACLs that include ACEs with permit actions only.



Question 7

Which of the following three statements are correct regarding IPv6 QoS?  (Choose three.)


  1. The traffic class field in the IPv6 header can be used to set specific precedence or DSCP values.
  2. A 20-bit flow label field enables per-flow processing.
  3. DS-TE is not supported by IPv6.
  4. Per-hop behavior in IPv6 networks is based on EXP bits.
  5. IPv6 QoS features are configured using the modular QoS CLI on Cisco routers.
Correct answer: ABE
Explanation:
http://www.cisco.com/en/US/technologies/tk648/tk872/technologies_white_paper0900aecd8026004d.pdfCisco Systems.             IPv6 QoS                                     AT-A-GLANCE RFC 2460/3697 Currently IPv6 provides support for QoS marking via a field in the IPv6 header. Similar to the type of service (ToS) field in the IPv4 header, the traffic class field (8 bits) is available for use by originating nodes and for forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets.      Current Cisco IOS Software support for IPv6 QoS includes:Packet classification Queuing (includes LLQ; excludes legacy PQ/CQ) Traffic shaping WRED IPv6 also has a 20-bit field known as the flow label field (RFC 3697). The flow label enables per flow processing for differentiation at the IP layer. It can be used for special sender requests and is set by the source node. The flow label must be modified by an intermediate mode. Planned Cisco IOS Software support for IPv6 QoS includes:Compressed Real-Time Protocol (cRTP) Network-based application recognition (NBAR) Committed access rate (CAR)
http://www.cisco.com/en/US/technologies/tk648/tk872/technologies_white_paper0900aecd8026004d.pdf
Cisco Systems.             IPv6 QoS 
                                    AT-A-GLANCE 
RFC 2460/3697 
Currently IPv6 provides support for QoS marking via a field in the IPv6 header. 
Similar to the type of service (ToS) field in the IPv4 header, the traffic class field (8 bits) is available for use by originating nodes and for forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets.  
  
Current Cisco IOS Software support for IPv6 QoS includes:
Packet classification 
Queuing (includes LLQ; excludes legacy PQ/CQ) 
Traffic shaping 
WRED 
IPv6 also has a 20-bit field known as the flow label field (RFC 3697). The flow label enables per flow processing for differentiation at the IP layer. 
It can be used for special sender requests and is set by the source node. 
The flow label must be modified by an intermediate mode. 
Planned Cisco IOS Software support for IPv6 QoS includes:
Compressed Real-Time Protocol (cRTP) 
Network-based application recognition (NBAR) 
Committed access rate (CAR)



Question 8

On the Cisco IOS XR, when using the match protocol command within a class-map to classify traffic, you noticed that the match protocol option on the Cisco IOS XR shows much fewer protocol options than on the Cisco IOS or IOS XE, like there is no option such as the match protocol yahoo-messenger command on the Cisco IOS XR. Why is this?


  1. because the Cisco IOS XR router does not have the correct software packages installed
  2. because when defining the class-map, the class-map type should be set to type inspect: class-map type inspect class-map-name command
  3. because NBAR is not supported on the Cisco IOS XR
  4. because flexible packet matching has not been enabled on the Cisco IOS XR router
Correct answer: C



Question 9

Which three steps are required to configure QPPB on Cisco IOS XR routers? (Choose three.)


  1. Apply a QPPB route policy to the BGP process using the table-policy command
  2. Apply a QPPB route policy to the BGP neighbor using the route-policy command
  3. Define a QPPB route policy to match the customer routes, then set the IP precedence or qos-group
  4. Define a QPPB route policy to match the customer IP precedence or qos-group markings, then set the BGP community
  5. Enable QPPB on an interface using the ipv4 bgp policy propagation input ip-precedence|qos-group destination|source command
  6. Enable QPPB on an interface using the ipv4 bgp policy propagation output ip-precedence|qos-group destination|source command
Correct answer: ACE
Explanation:
QoS Policy Propagation via BGP (QPPB), is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol (BGP), thus helping to classify based on destination instead of source address.
QoS Policy Propagation via BGP (QPPB), is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol (BGP), thus helping to classify based on destination instead of source address.



Question 10

The Cisco IOS and IOS XE qos pre-classify command allows which kind of packet classification on IP packets that are encapsulated with GRE and IPsec?


  1. allows for packets to be classified based on the ToS byte values before packet encryption
  2. allows for packets to be classified based on the ToS byte values after packet encryption
  3. allows for packets to be classified based on the packet payload before packet encryption
  4. allows for packets to be classified based on the packet payload after packet encryption
  5. allows for packets to be classified based on the packet header parameters other than the ToS byte values after packet encryption
Correct answer: A
Explanation:
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtmlThe qos pre-classify command When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur. In this example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:Router(config)# interface tunnel0 Router(config-if)# qos pre-classify
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtml
The qos pre-classify command 
When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur. 
In this example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:
Router(config)# interface tunnel0 
Router(config-if)# qos pre-classify



Question 11

On a Cisco IOS XR router, which mechanism protects the router resources by filtering and policing the packets flows that are destined to the router that is based on defined flow-type rates?


  1. LLQ
  2. LPTS
  3. Committed Access Rate
  4. Control Plane Policing
  5. Management Plane Protection
  6. NetFlow
  7. ACL
Correct answer: B
Explanation:
Local Packet Transport Services (LPTS) maintains tables describing all packet flows destined for the secure domain router (SDR), making sure that packets are delivered to their intended destinations. The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).
Local Packet Transport Services (LPTS) maintains tables describing all packet flows destined for the secure domain router (SDR), making sure that packets are delivered to their intended destinations. 
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).



Question 12

When configuring LLQ (strict priority queue) on a traffic class using the Cisco IOS XR priority command on a Cisco ASR9K router, which additional QoS command is required for this traffic class?


  1. shape
  2. police
  3. random-detect
  4. bandwidth
Correct answer: B
Explanation:
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).
The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ).



Question 13

When implementing MPLS DS-TE on Cisco IOS XR routers, all aggregate Cisco MPLS TE traffic is mapped to which class type by default?


  1. class-type 0 (bandwidth global pool)
  2. class-type 1 (bandwidth subpool)
  3. class-type 2 (bandwidth priority)
  4. class type class-default (bandwidth best-effort)
Correct answer: A
Explanation:
Differentiated Services Traffic Engineering MPLS Differentiated Services (Diff-Serv) Aware Traffic Engineering (DS-TE) is an extension of the regular MPLS-TE feature. Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. To support various classes of service (CoS), users can configure multiple bandwidth constraints. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint. MPLS diff-serv traffic engineering provides the ability to configure multiple bandwidth constraints on an MPLSenabled interface. Available bandwidths from all configured bandwidth constraints are advertised using IGP. TE tunnel is configured with bandwidth value and class-type requirements. Path calculation and admission control take the bandwidth and class-type into consideration. RSVP is used to signal the TE tunnel with bandwidth and class-type requirements. Diff-Serv TE can be deployed with either Russian Doll Model (RDM) or Maximum Allocation Model (MAM) for bandwidth calculations.  TE Class Mapping Each of the eight available bandwidth values advertised in the IGP corresponds to a TE Class. Because the IGP advertises only eight bandwidth values, there can be a maximum of only eight TE classes supported in an IETF DS-TE network. TE class mapping must be exactly the same on all routers in a DS-TE domain. It is the responsibility of the operator configure these settings properly as there is no way to automatically check or enforce consistency. The operator must configure TE tunnel class types and priority levels to form a valid TE class. When the TE class map configuration is changed, tunnels already up are brought down. Tunnels in the down state, can be set up if a valid TE class map is found. Table 4 TE Classes and Priority     The default mapping includes four classes types.
Differentiated Services Traffic Engineering 
MPLS Differentiated Services (Diff-Serv) Aware Traffic Engineering (DS-TE) is an extension of the regular MPLS-TE feature. Regular traffic engineering does not provide bandwidth guarantees to different traffic classes. A single bandwidth constraint is used in regular TE that is shared by all traffic. To support various classes of service (CoS), users can configure multiple bandwidth constraints. These bandwidth constraints can be treated differently based on the requirement for the traffic class using that constraint. 
MPLS diff-serv traffic engineering provides the ability to configure multiple bandwidth constraints on an MPLSenabled interface. Available bandwidths from all configured bandwidth constraints are advertised using IGP. 
TE tunnel is configured with bandwidth value and class-type requirements. Path calculation and admission control take the bandwidth and class-type into consideration. RSVP is used to signal the TE tunnel with bandwidth and class-type requirements. 
Diff-Serv TE can be deployed with either Russian Doll Model (RDM) or Maximum Allocation Model (MAM) for bandwidth calculations. 
TE Class Mapping 
Each of the eight available bandwidth values advertised in the IGP corresponds to a TE Class. Because the IGP advertises only eight bandwidth values, there can be a maximum of only eight TE classes supported in an IETF DS-TE network. 
TE class mapping must be exactly the same on all routers in a DS-TE domain. It is the responsibility of the operator configure these settings properly as there is no way to automatically check or enforce consistency. 
The operator must configure TE tunnel class types and priority levels to form a valid TE class. When the TE class map configuration is changed, tunnels already up are brought down. Tunnels in the down state, can be set up if a valid TE class map is found. 
Table 4 TE Classes and Priority 
  
The default mapping includes four classes types.



Question 14

On the Cisco IOS XR, which MQC configuration is different than on the Cisco IOS and IOS XE?


  1. On the Cisco IOS XR, WRED can only be applied in the output direction.
  2. On the Cisco IOS XR, marking can only be applied in the input direction.
  3. On the Cisco IOS XR, LLQ can be applied in the input or output direction.
  4. On the Cisco IOS XR, LLQ can use up to four priority queues: level 1, level 2, level 3, and level 4.
Correct answer: C



Question 15

Refer to the Cisco IOS XR policy-map configuration exhibit. 
  
What is wrong with the policy-map configuration?


  1. missing the priority percent command under class one and class two
  2. missing the police command under class one and class two
  3. missing the police command under class three
  4. missing the priority bandwidth command under class one and class two
  5. missing the bandwidth command under class one and class two
Correct answer: B
Explanation:
Hierarchical policing is also supported. In such a configuration, both parent and child policies have class-maps containing policing statements, as in the following example:! policy-map child class gold police rate percent 50 conform-action set precedence immediate exceed-action drop ! ! policy-map parent class match_all police rate 10000 kbps burst 15000 exceed-action drop service-policy child
Hierarchical policing is also supported. In such a configuration, both parent and child policies have class-maps 
containing policing statements, as in the following example:
policy-map child 
class gold 
police rate percent 50 conform-action set precedence immediate exceed-action 
drop 
policy-map parent 
class match_all 
police rate 10000 kbps burst 15000 exceed-action drop 
service-policy child



Question 16

When configuring class-based WRED on Cisco routers, which WRED parameter is not user configurable on a Cisco IOS XR but is user configurable on a Cisco IOS and IOS XE?


  1. the ingress or egress direction where the class-based WRED policy will be applied
  2. the maximum threshold
  3. the minimum threshold
  4. the mark probability denominator
Correct answer: D
Explanation:
Comparison of Cisco IOS QoS and Cisco IOS-XR QoS The Cisco IOS-XR software implementation of QoS is basically the same as the QoS implementation on Cisco IOS software, with the following exceptions:On Cisco IOS-XR software, the bandwidth command can be configured only in egress policies. The following changes have been made to the class-map command on Cisco IOS-XR software:Supports 4K per logical router. Maximum number of match criteria configurable in one class map is eight. When a class is marked as high priority using the priority command on Cisco IOS-XR software, we recommend that you configure a policer to limit the priority traffic. Limiting the priority traffic will ensure that the priority traffic does not starve all of the other traffic on the line card. Use the police command to explicitly configure the policer. On Cisco IO-XR software, only one conform-action, exceed-action, or violate-action command can be configured at a time. To configure traffic policing, use the police command. On Cisco IOS-XR software, policy modifications cannot be made on existing policies. Use the policy-map command to remove the policy from all attached interfaces, delete the policy map, and redefine a new policy. When configuring a policy map on Cisco IOS-XR software, the maximum number of classes configurable in one policy map is 16, which includes both Level 1 and Level 2 classes. To configure a policy map, use the policy-map command. When WRED is configured on Cisco IOS-XR software, the mark probability in the random-detect command is not configurable—it is always set to 1. When the random-detect exp command is used on Cisco IOS-XR software, the exponential weighting constant is not configurable and will be programmed automatically by Cisco IOS-XR software. When access control lists (ACLs) are used in QoS class maps, the underlying deny or permit actions associated with access control entries (ACEs) are ignored. ACEs are used as a classification mechanism in order to provide appropriate QoS behavior as specified in class maps. Use ACLs that include ACEs with permit actions only.
Comparison of Cisco IOS QoS and Cisco IOS-XR QoS 
The Cisco IOS-XR software implementation of QoS is basically the same as the QoS implementation on Cisco 
IOS software, with the following exceptions:
  • On Cisco IOS-XR software, the bandwidth command can be configured only in egress policies. 
  • The following changes have been made to the class-map command on Cisco IOS-XR software:
    • Supports 4K per logical router. 
    • Maximum number of match criteria configurable in one class map is eight. 
  • When a class is marked as high priority using the priority command on Cisco IOS-XR software, we recommend that you configure a policer to limit the priority traffic. Limiting the priority traffic will ensure that the priority traffic does not starve all of the other traffic on the line card. Use the police command to explicitly configure the policer. 
  • On Cisco IO-XR software, only one conform-action, exceed-action, or violate-action command can be configured at a time. To configure traffic policing, use the police command. 
  • On Cisco IOS-XR software, policy modifications cannot be made on existing policies. Use the policy-map command to remove the policy from all attached interfaces, delete the policy map, and redefine a new policy. 
  • When configuring a policy map on Cisco IOS-XR software, the maximum number of classes configurable in one policy map is 16, which includes both Level 1 and Level 2 classes. To configure a policy map, use the policy-map command. 
  • When WRED is configured on Cisco IOS-XR software, the mark probability in the random-detect command is not configurable—it is always set to 1. 
  • When the random-detect exp command is used on Cisco IOS-XR software, the exponential weighting constant is not configurable and will be programmed automatically by Cisco IOS-XR software. 
  • When access control lists (ACLs) are used in QoS class maps, the underlying deny or permit actions associated with access control entries (ACEs) are ignored. ACEs are used as a classification mechanism in order to provide appropriate QoS behavior as specified in class maps. Use ACLs that include ACEs with permit actions only.



Question 17

Which of the following three statements are correct regarding IPv6 QoS?  (Choose three.)


  1. The traffic class field in the IPv6 header can be used to set specific precedence or DSCP values.
  2. A 20-bit flow label field enables per-flow processing.
  3. DS-TE is not supported by IPv6.
  4. Per-hop behavior in IPv6 networks is based on EXP bits.
  5. IPv6 QoS features are configured using the modular QoS CLI on Cisco routers.
Correct answer: ABE
Explanation:
http://www.cisco.com/en/US/technologies/tk648/tk872/technologies_white_paper0900aecd8026004d.pdfCisco Systems.             IPv6 QoS                                     AT-A-GLANCE RFC 2460/3697 Currently IPv6 provides support for QoS marking via a field in the IPv6 header. Similar to the type of service (ToS) field in the IPv4 header, the traffic class field (8 bits) is available for use by originating nodes and for forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets.      Current Cisco IOS Software support for IPv6 QoS includes:Packet classification Queuing (includes LLQ; excludes legacy PQ/CQ) Traffic shaping WRED IPv6 also has a 20-bit field known as the flow label field (RFC 3697). The flow label enables per flow processing for differentiation at the IP layer. It can be used for special sender requests and is set by the source node. The flow label must be modified by an intermediate mode. Planned Cisco IOS Software support for IPv6 QoS includes:Compressed Real-Time Protocol (cRTP) Network-based application recognition (NBAR) Committed access rate (CAR)
http://www.cisco.com/en/US/technologies/tk648/tk872/technologies_white_paper0900aecd8026004d.pdf
Cisco Systems.             IPv6 QoS 
                                    AT-A-GLANCE 
RFC 2460/3697 
Currently IPv6 provides support for QoS marking via a field in the IPv6 header. 
Similar to the type of service (ToS) field in the IPv4 header, the traffic class field (8 bits) is available for use by originating nodes and for forwarding routers to identify and distinguish between different classes or priorities of IPv6 packets.  
  
Current Cisco IOS Software support for IPv6 QoS includes:
Packet classification 
Queuing (includes LLQ; excludes legacy PQ/CQ) 
Traffic shaping 
WRED 
IPv6 also has a 20-bit field known as the flow label field (RFC 3697). The flow label enables per flow processing for differentiation at the IP layer. 
It can be used for special sender requests and is set by the source node. 
The flow label must be modified by an intermediate mode. 
Planned Cisco IOS Software support for IPv6 QoS includes:
Compressed Real-Time Protocol (cRTP) 
Network-based application recognition (NBAR) 
Committed access rate (CAR)



Question 18

On the Cisco IOS XR, when using the match protocol command within a class-map to classify traffic, you noticed that the match protocol option on the Cisco IOS XR shows much fewer protocol options than on the Cisco IOS or IOS XE, like there is no option such as the match protocol yahoo-messenger command on the Cisco IOS XR. Why is this?


  1. because the Cisco IOS XR router does not have the correct software packages installed
  2. because when defining the class-map, the class-map type should be set to type inspect: class-map type inspect class-map-name command
  3. because NBAR is not supported on the Cisco IOS XR
  4. because flexible packet matching has not been enabled on the Cisco IOS XR router
Correct answer: C



Question 19

Which three steps are required to configure QPPB on Cisco IOS XR routers? (Choose three.)


  1. Apply a QPPB route policy to the BGP process using the table-policy command
  2. Apply a QPPB route policy to the BGP neighbor using the route-policy command
  3. Define a QPPB route policy to match the customer routes, then set the IP precedence or qos-group
  4. Define a QPPB route policy to match the customer IP precedence or qos-group markings, then set the BGP community
  5. Enable QPPB on an interface using the ipv4 bgp policy propagation input ip-precedence|qos-group destination|source command
  6. Enable QPPB on an interface using the ipv4 bgp policy propagation output ip-precedence|qos-group destination|source command
Correct answer: ACE
Explanation:
QoS Policy Propagation via BGP (QPPB), is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol (BGP), thus helping to classify based on destination instead of source address.
QoS Policy Propagation via BGP (QPPB), is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party based on access lists, community lists and autonomous system paths in the Border Gateway Protocol (BGP), thus helping to classify based on destination instead of source address.



Question 20

The Cisco IOS and IOS XE qos pre-classify command allows which kind of packet classification on IP packets that are encapsulated with GRE and IPsec?


  1. allows for packets to be classified based on the ToS byte values before packet encryption
  2. allows for packets to be classified based on the ToS byte values after packet encryption
  3. allows for packets to be classified based on the packet payload before packet encryption
  4. allows for packets to be classified based on the packet payload after packet encryption
  5. allows for packets to be classified based on the packet header parameters other than the ToS byte values after packet encryption
Correct answer: A
Explanation:
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtmlThe qos pre-classify command When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur. In this example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:Router(config)# interface tunnel0 Router(config-if)# qos pre-classify
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a008017405e.shtml
The qos pre-classify command 
When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. With the introduction of the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before tunneling and encryption occur. 
In this example, tunnel0 is the tunnel name. The qos pre-classify command enables the QoS for VPNs feature on tunnel0:
Router(config)# interface tunnel0 
Router(config-if)# qos pre-classify









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