Quality of Service (QoS): Managing Bandwidth More Effectively

QoS Operating Notes and Restrictions

QoS Operating Notes and RestrictionsTable 6-11. Details of Packet Criteria and Restrictions for QoS Support

Packet Criteria or Restriction

 

QoS Types

 

DSCP Overwrite

 

 

 

 

(Re-Marking)

 

 

 

 

 

 

IP Type-of-Service

Source Port

Incoming 802.1p

 

 

 

 

 

 

Restricted to IPv4 Packets Only

Yes

No

No

Yes

 

 

 

 

 

Allow Packets with IP Options1

Yes

Yes

Yes

Yes

Support IPv6 Packets2

No

Yes

Yes

No

Support Layer-2 SAP Encapsulation

No

Yes

Yes

No

1An “IP Option” is an optional, extra field in the header of an IP packet. If the switch is configured with a UDP/TCP type and a packet with an IP option is received, the switch uses the next-highest type, if configured.

2All Switches: For explicit QoS support of IPv6 packets, force IPv6 traffic into its own set of VLANs and then configure VLAN-based types for those VLANs.

For Devices that Do Not Support 802.1Q VLAN-Tagged Ports: For communication between these devices and the switch, connect the device to a switch port configured as Untagged for the VLAN in which you want the device’s traffic to move.

Port Tagging Rules: For a port on the switch to be a member of a VLAN, the port must be configured as either Tagged or Untagged for that VLAN. For more on VLANs, refer to chapter 2, “Static Virtual LANs (VLANs)”.

SAP-Encapsulated Packet Restriction: Except for source-port QoS and VLAN QoS, the switches covered in this guide do not support QoS operation for SAP-Encapsulated packets. Thus, the switch can use only VLAN QoS and source-port QoS to prioritize SAP-encapsu- lated packets.

RADIUS Authentication: RADIUS authentication allowing traffic through a given port may override the port’s QoS configuration, which generates an Event Log message. When the authenticated host discon- nects, the port returns to the static QoS configuration.

Not Supported: Use of an inbound 802.1p packet priority as a type for remapping a packet’s outbound priority to different 802.1p priority. For example, where inbound packets carry an 802.1p priority of 1, QoS cannot be configured to use this priority as a type for changing the outbound priority to 0.

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