Quality of Service (QoS): Managing Bandwidth More Effectively

IP Multicast (IGMP) Interaction with QoS

IP Multicast (IGMP) Interaction withQoS

IGMP high-priority-forward causes the switch to service the subscribed IP multicast group traffic at high priority, even if QoS on the switch has relegated the traffic to a lower priority. This does not affect any QoS priority settings, so the QoS priority is honored by downstream devices. However, QoS does take precedence over IGMP normal-priority traffic.

The switch’s ability to prioritize IGMP traffic for either a normal or high priority outbound queue overrides any QoS criteria, and does not affect any 802.1p priority settings the switch may assign. For a given packet, if both IGMP high priority and QoS are configured, the QoS classification occurs and the switch marks the packet for downstream devices, but the packet is serviced by the high-priority queue when leaving the switch.

IGMP High

QoS Configuration

Switch Port Output

Outbound 802.1p Setting

Priority

Affects Packet

Queue

(Requires Tagged VLAN)

 

 

 

 

Not Enabled

Yes

Determined by QoS

Determined by QoS

 

 

 

 

Enabled

See above para-

High

As determined by QoS if QoS is

 

graph.

 

active.

 

 

 

 

QoS Messages in the CLI

Message

Meaning

DSCP Policy < decimal-codepoint> not

You have attempted to map a QoS type to a

configured

codepoint for which there is no configured

 

priority (No-override). Use the qos dscp-map

 

command to configure a priority for the

 

codepoint, then map the type to the

 

codepoint.

Cannot modify DSCP Policy < codepoint > - in use by other qos rules.

You have attempted to map a QoS type to a codepoint that is already in use by other QoS types. Before remapping the codepoint to a new priority, you must reconfigure the other QoS types so that they do not use this codepoint. You can have multiple QoS types use this same codepoint as long as it is acceptable for all such types to use the same priority.

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