Configuration Guide User guide

FastIron Configuration Guide 1981

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DSCP-based QoS configuration

Brocade IronWare releases support basic DSCP-based QoS (also called Type of Service (ToS)-based

QoS) as described in this chapter. However, the FastIron family of switches does not support other

advanced DSCP-based QoS features as described in the Enterprise Configuration and

Management Guide.

Brocade IronWare releases also support marking of the DSCP value. The software can read Layer 3

Quality of Service (QoS) information in an IP packet and select a forwarding queue for the packet

based on the information. The software interprets the value in the six most significant bits of the IP

packet header 8-bit ToS field as a DSCP value, and maps that value to an internal forwarding

priority.

The internal forwarding priorities are mapped to one of the eight forwarding queues (qosp0 through

qosp7) on the Brocade device. During a forwarding cycle, the device gives more preference to the

higher-numbered queues, so that more packets are forwarded from these queues. For example,

queue qosp7 receives the highest preference, while queue qosp0, the best-effort queue, receives

the lowest preference.

Application notes for DSCP-based QoS

• DSCP-based QoS is not automatically honored for routed and switched traffic. The default is

802.1p to CoS mapping. To honor DSCP-based QoS, you must either use an ACL or enable trust

DSCP. Refer to “Using ACLs to honor DSCP-based QoS” on page 1981.

• When DSCP marking is enabled, the device changes the contents of the inbound packet ToS

field to match the DSCP-based QoS value. This differs from BigIron, which marks the outbound

packet ToS field.

Using ACLs to honor DSCP-based QoS

This section shows how to configure Brocade devices to honor DSCP-based QoS for routed and

switched traffic.

FastIron stackable devices

FastIron WS and Brocade FCX Series devices support DSCP-based QoS on a per-port basis.

DSCP-based QoS is not automatically honored for switched traffic. The default is 802.1p to CoS

mapping. To honor DSCP-based QoS, enter the following command at the interface level of the CLI.

[no] trust dscp

To disable the configuration, use the no form of the command.

When trust dscp is enabled, the interface honors the Layer 3 DSCP value. By default, the interface

honors the Layer 2 CoS value.

NOTE

The trust dscp command is not supported with 802.1p priority override.