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Zorluk: OrtaQoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

A network administrator is designing a QoS marking policy to classify enterprise application traffic across both Layer 2 switch trunks and Layer 3 routed WAN links. Which statement accurately compares Class of Service (CoS) and Differentiated Services Code Point (DSCP) markings?

  1. CoS relies on a 3-bit field located inside the 802.1Q VLAN tag, whereas DSCP uses a 6-bit field inside the IP header.Cevap
  2. B
    CoS uses a 6-bit field in the IP header, whereas DSCP uses a 3-bit Priority Code Point field in the Ethernet frame header.
  3. C
    CoS automatically buffers non-conforming bursty traffic in queues, whereas DSCP drops out-of-profile traffic at ingress.
  4. D
    CoS markings persist end-to-end across Layer 3 router hops, whereas DSCP markings are stripped when packets cross ethernet switches.

Cevap

Class of Service (CoS) relies on a 3-bit Priority Code Point (PCP) field within the Layer 2 802.1Q VLAN header, whereas Differentiated Services Code Point (DSCP) uses a 6-bit field within the Layer 3 IP header.
The statement identifying CoS as a 3-bit field inside the 802.1Q VLAN header and DSCP as a 6-bit field in the IP header is correct. CoS provides 8 priority levels (0 to 7) for Layer 2 tagged frames, while DSCP provides 64 values (0 to 63) in the Differentiated Services field of Layer 3 IP headers.

Adım Adım Çözüm

1
Identify Layer 2 QoS classification mechanisms.
CoS (Class of Service / 802.1p) is defined in the 3-bit Priority Code Point field of an 802.1Q VLAN frame header, giving 8 possible priority levels (0-7).
Layer 2 headers are encapsulated per link and only exist on tagged Ethernet frames.
2
Identify Layer 3 QoS classification mechanisms.
DSCP (Differentiated Services Code Point) is defined in the 6-bit DiffServ field of the IPv4/IPv6 packet header, giving 64 possible code points (0-63).
Layer 3 headers persist across router hops end-to-end from source to destination.
3
Compare header locations and persistence capabilities.
CoS is restricted to tagged Layer 2 Ethernet trunks and is stripped by routers, while DSCP travels inside the IP packet across routed boundaries.
Routers decapsulate Layer 2 frames when forwarding IP packets, removing the 802.1Q tag containing CoS.

Anahtar Kavram

QoS Marking Fields (CoS 3-bit L2 vs DSCP 6-bit L3)
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Konular

QoS Per-Hop Behaviors, Classification, Marking, Queuing, and Traffic Shaping/Policing

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