300-070 Question #72: Real Exam Question with Answer & Explanation

The correct answer is A. switch. Layer 2 to Layer 3 QoS mapping is configured on a switch. Layer 2 QoS uses the Class of Service (CoS) value in the 802.1Q VLAN tag (3-bit field in the Ethernet frame header). Layer 3 QoS uses DSCP (Differentiated Services Code Point) or IP Precedence values in the IP packet heade

Quality of Service

Question

On what equipment do you configure Layer 2 to Layer 3 QoS mapping?

Options

Aswitch
Brouter
Cfirewall
DCisco Unified Communications Manager
Ebridge

Explanation

Layer 2 to Layer 3 QoS mapping is configured on a switch. Layer 2 QoS uses the Class of Service (CoS) value in the 802.1Q VLAN tag (3-bit field in the Ethernet frame header). Layer 3 QoS uses DSCP (Differentiated Services Code Point) or IP Precedence values in the IP packet header. When a frame arrives at a switch, the switch can map the incoming CoS value to the appropriate DSCP value (or vice versa) to maintain QoS markings as traffic transitions between Layer 2 segments and Layer 3 routed segments. Routers handle Layer 3 QoS but don't perform L2-to-L3 mapping. Firewalls and CUCM are not responsible for this translation. Bridges operate at Layer 2 only.

Topics

#QoS mapping#Layer 2 to Layer 3#CoS to DSCP#switch

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