All flows that are not explicitly dropped by the Route Policy are subject to DSCP marking by the QoS Policy. DSCP markings specify end-to-end QoS policies throughout a network.
As with all policies, the appliance searches sequentially through the policy for the first MATCH criteria that applies. If no entries match, then ultimately the default entry applies. For the QoS Policy, the default DSCP values for LAN QoS and WAN QoS are trust-lan.
The appliance encapsulates optimized traffic. This process adds an IP outer header to packets for travel across the WAN. However, because pass-through traffic doesn’t receive this additional header, its handling is different. The following two sections provide illustrated examples:
This section illustrates and explains how the appliance applies the QoS Policy to optimized traffic in the following scenarios:
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Based on MATCH criteria, the QoS Policy applies the LAN QoS setting of trust-lan, leaving the LAN DSCP markings as be (best effort). As the packet is encapsulated, this is now part of the IP inner header.
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Since the WAN QoS is trust-lan, the appliance also sets the WAN QoS bits to be in the encapsulating IP outer header.
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When the packet reaches the destination appliance, the appliance de-encapsulates the packet, and the packet traverses the LAN with the DSCP markings set to be.
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Based on MATCH criteria, the QoS Policy changes the LAN QoS setting to ef (express forwarding). As the packet is encapsulated, this is now part of the IP inner header.
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Since the policy’s WAN QoS is trust-lan, the appliance refers back to the original DSCP markings and sets the WAN QoS bits to be in the encapsulating IP outer header.
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When the packet reaches the destination appliance, the appliance de-encapsulates the packet, and the packet traverses the LAN with the DSCP markings set to ef.
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Based on MATCH criteria, the QoS Policy applies the LAN QoS setting of trust-lan, leaving the LAN DSCP markings as be (best effort). As the packet is encapsulated, this is now part of the IP inner header.
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Since the policy’s WAN QoS action is cs5 (class selector 5), the appliance sets the bits to cs5 in the encapsulating IP outer header.
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When the packet reaches the destination appliance, the appliance de-encapsulates the packet, and the packet traverses the LAN with the DSCP markings set to be.
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Based on MATCH criteria, the QoS Policy changes the LAN QoS setting to ef. As the packet is encapsulated, this is now part of the IP inner header.
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Since the policy’s WAN QoS action is cs5, the appliance sets the bits to cs5 in the encapsulating IP outer header.
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When the packet reaches the destination appliance, the appliance de-encapsulates the packet, and the packet traverses the LAN with the DSCP markings set to ef.
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The appliance applies the QoS Policy’s DSCP markings to all pass-through flows — whether shaped or unshaped — in the same way:
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If there is a trust-lan setting in the policy match, it is ignored.
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To summarize, all pass-through traffic is trust-lan unless it’s modified by the WAN QoS setting. When that’s the case, the packet retains the modified QoS setting as it travels through the WAN to the destination appliance.
The following three examples illustrate how the QoS Policy’s LAN QoS and WAN QoS settings affect a matched flow’s DSCP markings:
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When the packet reaches the destination appliance, it retains the be setting as the LAN receives it.
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When the packet reaches the destination appliance, it retains the be setting as the LAN receives it.
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When the packet reaches the destination appliance, it retains the cs5 setting as the LAN receives it.
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When the packet reaches the destination appliance, it retains the cs5 setting as the LAN receives it.
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Following is a list of definitions for the available Differentiated Services Code Point (DSCP) markings, which use a 6-bit value to indicate Per-Hop Behavior (PHB):
