I'm go with Answer B
The QoS Policy Propagation via BGP feature allows you to classify packets by IP precedence based on the Border Gateway Protocol (BGP) Attributes like community lists, BGP autonomous system paths, and access lists.
I don't agree with you, because of how the answer is frased " QoS policies rely exclusively on BGP attributes to manipulate traffic". "exclusively" rules out the access-list. So it cannot be b. Therefor d makes more sens
In this question it is basing off of the qos policy applied... in the policy the condition is set match on as-path which is a bgp attribute. There are no other match criteria here so BGP is the only thing this policy cares about.
A - incorrect because qos-group can only be applied to ingress
B - This is the only one that makes sense
C - Irrelevant .. .nothing about the question says MPLS.
D - How does this allow us to gain full coverage on the network?
Also note the attach point of the policy. We are applying it to BGP tables... i am not super familiar with table policies...
I came to the same conclusion on this paraphase:
Packet classification identifies and marks traffic flows that require congestion management or congestion avoidance on a data path. Quality-of-service Policy Propagation Using Border Gateway Protocol (QPPB) allows you to classify packets by Qos Group ID, based on access lists (ACLs), Border Gateway Protocol (BGP) community lists, BGP autonomous system (AS) paths, Source Prefix address, or Destination Prefix address. After a packet has been classified, you can use other QoS features such as policing and weighted random early detection (WRED) to specify and enforce policies to fit your business model
Found this:
In short the purpose of QPPB is to allow packet classification based on BGP attributes.
From: https://community.cisco.com/t5/service-providers-knowledge-base/asr9000-xr-implementing-qos-policy-propagation-for-bgp-qppb/ta-p/3136639
Therefore... I will stick wtih B as the answer... I jsut don't get the "gains full coverage on the network" from answer D and thus i can't accept that as an answer.
I change to D based on Cisco book quote from jmbp12 :
"QPPB allows BGP policy set in one location of the network to be propagated via BGP to other parts of the network, where appropriate QoS policies can be created."
D is the correct
Packet classification identifies and marks traffic flows that require congestion management or congestion avoidance on a data path. Quality-of-service Policy Propagation Using Border Gateway Protocol (QPPB) allows you to classify packets by Qos Group ID, based on access lists (ACLs), Border Gateway Protocol (BGP) community lists, BGP autonomous system (AS) paths, Source Prefix address, or Destination Prefix address. After a packet has been classified, you can use other QoS features such as policing and weighted random early detection (WRED) to specify and enforce policies to fit your business model.
https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r7-3/qos/b-qos-cg-asr9k-73x/config-mod-qos-packet-classification.html
B - the question asks "which statement supports QPPB implementation" so it is about QPPB in particular. In this case B is correct as QPPB uses BGP attributes (nothing else) to manipulate traffic:
From https://community.cisco.com/t5/service-providers-knowledge-base/asr9000-xr-implementing-qos-policy-propagation-for-bgp-qppb/ta-p/3136639
"In short the purpose of QPPB is to allow packet classification based on BGP attributes."
From Cisco BGP book:
QoS Policy Propagation via BGP (QPPB) lets you map BGP prefixes and attributes to CEF parameters that can be used to enforce traffic policing. Compared to other QoS methods, QPPB allows BGP policy set in one location of the network to be propagated via BGP to other parts of the network, where appropriate QoS policies can be created.
"D" seems to be the correct answer.
i agree that QoS policies rely on BGP attributes, but EXCLUSIVELY... you can also use src/destination https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/qos/66x/b-qos-cg-ncs5500-66x/b-qos-cg-ncs5500-66x_chapter_010.html#id_77442
A can also be correct: "It can be used as a match criteria in an egress policy to set up various fields on the outgoing packet or shape flows." https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/qos/72x/b-qos-cg-ncs5500-72x/b-qos-cg-ncs5500-72x_chapter_010.html#id_77442"
D - https://www.ciscopress.com/articles/article.asp?p=169556&seqNum=5
QoS Policy Propagation via BGP (QPPB) lets you map BGP prefixes and attributes to CEF parameters that can be used to enforce traffic policing. Compared to other QoS methods, QPPB allows BGP policy set in one location of the network to be propagated via BGP to other parts of the network, where appropriate QoS policies can be created.
The policing can be done on the input to the router for traffic destined for 172.16.0.0 or on the output from the router for the return traffic sourced from 172.16.0.0. The policing is created based on the result of the policy lookup and settings done previously.
QPPB allows you to classify packets based on:
Access lists.
BGP community lists. You can use community lists to create groups of communities to use in a match clause of a route policy. As with access lists, you can create a series of community lists.
BGP autonomous system paths. You can filter routing updates by specifying an access list on both incoming and outbound updates, based on the BGP autonomous system path.
Source Prefix address. You can classify a set of prefixes coming from the address of a BGP neighbor(s).
Destination Prefix address. You can classify a set of BGP prefixes.
https://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k-r6-2/qos/configuration/guide/b-qos-cg-asr9000-62x/b-qos-cg-asr9000-62x_chapter_0110.html#ID2819
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