About QoS

QoS operation

On the switches covered in this guide, QoS operation may be configured through a combination of the following methods:

  • Globally-configured, switch-wide QoS settings

  • Classifier-based per-port and per-VLAN QoS policies.

Classifier-based QoS policies are designed to work with existing globally-configured, switch-wide QoS settings by allowing you to zoom in on a subset of port or VLAN traffic to further manage it. You can use multiple match criteria to more finely select and define the classes of traffic that you want to manage. QoS policy actions determine how you can handle the selected traffic.


[NOTE: ]

NOTE: While providing greater control for implementing QoS policies, classifier-based QoS policies may override globally-configured QoS settings.

Carefully plan your QoS strategies in advance, identifying the network traffic that you can globally configure and the traffic on which you want to execute customized, classifier-based QoS actions.


Globally-configured QoS

Globally-configured QoS operation supports the following types of packet classification and traffic marking on outbound port and VLAN traffic.

  • Globally configured packet classification criteria include:

    • IPv4 device: source and destination address

    • Layer 2 802.1p priority (VLAN header)

    • Layer 3 protocol (such as ARP, IP, IPX, RIP)

    • Layer 3 IPv4 Type of Service (ToS) byte: IP precedence or DSCP bits

    • Layer 3 IPv6 Traffic Class byte: IP precedence or DSCP bits

    • Layer 4 UDP/TCP application port

    • Source port on the switch

    • VLAN ID

  • Traffic marking options are as follows:

    • Setting the Layer 2 802.1p priority value in VLAN-tagged and untagged packet headers

    • Setting the Layer 3 Differentiated Services Codepoint (DSCP) bits in the ToS byte of IPv4 packet headers and Traffic Class byte of IPv6 headers.

Classifier-based QoS

Starting in release K.14.01, classifier-based QoS operation provides additional QoS actions on a per-port and per-VLAN basis.

  • Classifier-based match criteria on inbound IPv4/IPv6 traffic include:

    • IP source address (IPv4 and IPv6)

    • IP destination address (IPv4 and IPv6)

    • IP protocol (such as ICMP or SNMP)

    • Layer 3 IP precedence bits

    • Layer 3 DSCP codepoint

    • Layer 4 UDP/TCP application port

    • VLAN ID

  • Classifier-based QoS policy actions on matching IPv4/IPv6 packets are as follows:

    • Setting Layer 2 802.1p priority value (class of service) in VLAN-tagged and untagged packet headers

    • Setting the Layer 3 IP precedence bits

    • Setting the Layer 3 Differentiated-Services Codepoint (DSCP) bits

    • Rate limiting inbound traffic on port and VLAN interfaces

QoS packet classification

To manage network traffic using QoS features, you must first classify (select) the packets you want to manage. You can use any combination of the following packet classification methods to select packets for QoS management:

  • Globally configured, switch-wide classification criteria

  • Classifier-based match criteria applied to inbound traffic on specific port and VLAN interfaces


[NOTE: ]

NOTE: Starting in software release K.14.01, global and classifier-based QoS policies support IPv6 and IPv4 packet classification.


Using multiple global criteria


[NOTE: ]

NOTE: HP recommends that you configure a minimum number of global QoS classifiers to prioritize a specific packet type. Increasing the number of enabled global QoS classifiers increases the complexity of possible outcomes and consumes switch resources.


The switches covered in this guide provide six types of globally-configured QoS classifiers (match criteria) to select packets for QoS traffic marking.

When multiple, global QoS classifiers are configured, a switch uses the highest-to-lowest search order shown in the following table to identify the highest-precedence classifier to apply to any given packet. When a match between a packet and a classifier is found, the switch applies the QoS policy configured for the classifier and the packet is handled accordingly.

Globally-configured packet classification: search order and precedence

Search order Precedence Global QoS classifier
1 1 (highest) UDP/TCP application type (port)
2 2 Device priority (destination or source IP address)
3 3 IP type of service: precedence and DSCP bit sets (IP packets only)
4 4 IP protocol (IP, IPX, ARP, AppleTalk, SNA, and NetBeui)
5 5 VLAN ID
6 6 Incoming source-port on the switch
Default 7 (lowest) The incoming 802.1p priority (present in tagged VLAN environments) is preserved if no global QoS classifier with a higher precedence matches.

[NOTE: ]

NOTE: On the switches covered in this guide, if the switch is configured with multiple global classifiers that match the same packet, the switch only applies the QoS marking configured for the QoS classifier with the highest precedence. In this case, the QoS configuration for another, lower-precedence classifier that matches is ignored.

For example, if QoS assigns a high priority to packets belonging to VLAN 100 and normal priority to all IP protocol packets, because the IP protocol priority (4) has precedence over the VLAN priority (5), IP protocol packets on VLAN 100 are set to normal priority.


Classifier-based match criteria

In classifier-based packet classification, match criteria provide a way to select the packets on which you want to execute QoS actions, such as rate limiting or 802.1p prioritization.

Match criteria are configured by creating a class of IPv4 orIPv6 traffic, which contains one or more match or ignore statements. A traffic class may be used by any classifier-based software feature, such as QoS or port mirroring.

By using classifier-based QoS, you can configure multiple match criteria that search multiple fields in packet headers to select the exact traffic you want to rate limit or prioritize for a port or VLAN interface. A classifier-based QoS policy is especially useful when you want to manage different types of traffic in the same way (for example, to prioritize both IP subnet and voice traffic).

QoS traffic marking

When you apply or reconfigure QoS actions for selected packets, QoS supports different types of traffic marking in globally-configured QoS settings and classifier-based per-port or per-VLAN QoS policies.

Globally-configured traffic marking

If a packet matches one of the globally-configured packet classifiers, QoS applies one of the following types of traffic marking to the outbound packet:

Layer 2 802.1p prioritization

Controls the outbound port-queue priority for traffic leaving the switch, and (if traffic exits through a VLAN-tagged port) sends the priority setting with the individual packets to downstream devices.

Layer 3 DSCP marking

Enables the switch to set, change, and honor prioritization policies by using the Differentiated Services (diff-serv) bits in the IPv4 ToS byte and IPv6 Traffic Class byte of packet headers.

Layer 2 802.1p prioritization

By setting a new 802.1p priority value, QoS allows you to control the priority of outbound packets moving through the switch. The Layer 2 802.1p priority setting in a packet header determines the outbound port queue to which the packet is sent.

By default, the switches covered in this guide have eight outbound traffic queues (0 through 7). A lower-numbered queue has a lower outbound priority; a higher-numbered queue has a higher outbound priority. Packets are transmitted from the switch port on the basis of their queue assignment and whether any higher queues are empty. (To increase bandwidth, you can reconfigure the switch to use four or two outbound queues.)

Configuring a new 802.1p priority value allows you to set the outbound priority queue to which a packet is sent. For example, you can configure an 802.1p priority of 0 through 7 for an outbound packet. When the packet is sent to a port, the QoS priority determines the outbound queue to which the packet is assigned as shown in the following table.

802.1p priority settings and outbound queue assignment

802.1p priority setting Outbound port queue
1 and 2 Low priority (1, 2)
0 or 3 Normal priority (3, 4)
4 and 5 Medium priority (5, 6)
6 and 7 High priority (7, 8)

If a packet is transmitted in an untagged-VLAN environment, the 802.1p priority settings in the preceding table control only the outbound queue to which the packet is sent on the local switch. Because no VLAN tag is used, an 802.1p priority value is not added to the 802.1Q field in the packet header for use by downstream devices.

However, if your network uses only one VLAN and does not require VLAN-tagged ports, you can preserve 802.1p priority settings in outbound traffic by configuring the ports on links between devices on which you want 802.1p priorities to be honored as tagged VLAN members.

If a packet is transmitted in an 802.1Q VLAN-tagged environment, the QoS-configured 802.1p setting is also added to the VLAN packet header as an 802.1p priority for use by downstream devices and applications.

In an 802.1Q VLAN environment with VLAN-tagged ports, if QoS is not configured on the switch but is configured on an upstream device, the priorities carried in the packets determine the outbound port queue on which packets are forwarded.

Mapping 802.1p priorities to outbound port queues on the switch and downstream devices

Configured 802.1p priority Outbound port queue in the switch 802.1p priority added to tagged VLAN packets exiting the switch Queue assignment in downstream devices with:
8 queues 4 queues 2 queues
1 Queue 1 1 (low priority) Queue 1 Queue 1 Queue 1
2 Queue 2 2 Queue 2
0 Queue 3 0 (normal priority) Queue 3 Queue 2
3 Queue 4 3 Queue 4
4 Queue 5 4 (medium priority) Queue 5 Queue 3 Queue 2
5 Queue 6 5 Queue 6
6 Queue 7 6 (high priority) Queue 7 Queue 4
7 Queue 8 7 Queue 8

[NOTE: ]

NOTE: You can reconfigure the QoS queue setting to change the number of outbound port queues in the switch from eight (default) to four or two queues.


Layer 3 DSCP marking

By changing or honoring the settings of the DSCP codepoint in IP packet headers, QoS allows you to control the DSCP and associated 802.1p priority values in outbound IP packets that are sent to downstream devices.

You can later configure downstream devices to read and use the DSCP policy that QoS sets. When marking the DSCP bits in IP packets, a QoS policy is not dependent on VLAN-tagged ports to carry 802.1p packet priorities to downstream devices.

When configuring a Layer 3 DSCP policy, specify:

  • Bit values for the DSCP codepoint (the upper six bits in the ToS/Traffic Class byte in IP packet headers), entered in either binary format, the decimal equivalent, or an ASCII standard (hexadecimal) name

  • An 802.1p priority value that is associated with the new DSCP bit values

    Certain DSCP codepoints (such as Assured Forwarding and Expedited Forwarding) have default 802.1p priorities.

A DSCP policy assigns a DSCP codepoint and 802.1p priority value to IPv4 and IPv6 packets. You can classify traffic on an edge switch and use Layer 3 DSCP-marking (instead of only 802.1p priority) to assign and preserve QoS policies on downstream devices. In this case, if you reconfigure the 802.1p priority associated with the DSCP codepoint, the new 802.1p assignment takes effect starting on the switch on which it is configured and is used in packets sent to downstream devices.

If you configure a different 802.1p priority for a DSCP codepoint, the new DSCP policy overrides the 802.1p priority value in packets which enter the switch with the specified codepoint. The Layer 2 802.1p priority setting (0 through 7) determines the outbound port queue to which a packet is sent.

VLAN and untagged VLAN environments

QoS operates in VLAN-tagged and untagged environments. If your network does not use multiple VLANs, you can still implement the 802.1Q VLAN capability to allow packets to carry an 802.1p priority to the next downstream device. To do so, configure the ports on links to other network devices as VLAN-tagged members.

In a tagged or untagged VLAN, you can also ensure that IPv4/IPv6 packets carry an 802.1p priority to downstream devices by configuring DSCP marking in the ToS/Traffic Class byte.

The following table summarizes the QoS options for traffic-marking in VLAN-tagged and untagged environments.

QoS traffic marking supported in tagged and untagged VLANs

QoS marking supported on outbound packets Port membership in VLANs
Tagged Untagged
Assign an 802.1p priority that determines the outbound port queue to which a packet is sent Supported Supported
Carry the 802.1p priority to the next downstream device Supported Not Supported
Carry a DSCP policy (DSCP codepoint[1] and associated 802.1p priority[2] ) to downstream devices Supported Supported

[1] DSCP marking (DSCP codepoint and associated 802.1p priority) are not supported on non-IP packets and packets selected using the following global QOS classifiers: Layer 3 Protocol and IP-Precedence. Also, in order for DSCP policy marking to be honored on a downstream device, the device must be configured to use the DSCP policy in IP packet headers.

[2] The 802.1p priority associated with a DSCP codepoint is used to determine the packet's outbound port queue. When used in a VLAN-tagged environment, an 802.1p priority is also carried in the 802.1Q field of outbound packet headers.

Classifier-based traffic marking

Classifier-based per-port or per-VLAN QoS policies support the following traffic-marking actions. Note that globally-configured QoS traffic marking (802.1p and DSCP prioritization), classifier-based QoS policies also support IP precedence and rate limiting.

Layer 2802.1p prioritization

Controls the outbound port queue priority for traffic leaving the switch, and (if traffic exits through a VLAN-tagged port) sends the priority setting in packet headers to downstream devices.

Layer 3 IP precedence-bitmarking

Enables the switch to set, change, and honor prioritization policies by using the IP precedence bits in the ToS byte of IPv4 packet headers and Traffic Class byte of IPv6 headers.

Layer 3 DSCP marking

Enables the switch to set, change, and honor prioritization policies by using the Differentiated Services (Diffserv) bits in the ToS byte of IPv4 headers and Traffic Class byte of IPv6 headers.

Rate limiting

Enables a port or VLAN interface to allow only the specified amount of bandwidth to be used for inbound traffic. When traffic exceeds the configured limit, it is dropped.


[NOTE: ]

NOTE: After you apply a classifier-based QoS policy on a port or VLAN interface:

  • The 802.1p (CoS) priority and DSCP codepoint marking applied to classified packets override any 802.1p and DSCP codepoint values that are globally-configured using the QoS commands.

  • The rate limit applied to classified packets overrides any globally configured rate limit globally-configured. See the Management and Configuration Guide for more information.




No override

By default, the show qos output for following global QoS classifiers may display No-override for QoS marking: IP Precedence, IP Diffserv, Layer-3 Protocol, VLAN ID, and Source-port. The command No-override means that the global QoS policy used to mark matching packets does not assign an 802.1p value.

  • IP packets received through a VLAN-tagged port are managed using the 802.1p priority they carry in the 802.1Q field in their headers.

  • VLAN-tagged packets received through an untagged port are handled by the switch with normal priority.

Show QoS command output

Viewing show qos outputshows the global QoS configurations on the switch that are configured with the VLAN ID classifier. Note that non-default 802.1p priorities have been configured for VLAN IDs 22 and 33; packets received on VLAN 1 are managed with the default settings, as described in the two bulleted items above.

Viewing show qos output

Viewing show qos output

Global QoS restrictions

This table shows the packet types supported by different global QoS classifiers and DSCP marking.

Restrictions for global QoS support

Type of packets supported Global QoS classifiers DSCP overwrite (re-marking)
  TCP/UDP IP Device IP Type-of-Service Layer 3 Protocol VLAN ID Source Port Incoming 802.1p  
IP packets (IPv4 andIPv6 [1]) only Yes Yes Yes No No No No Yes
Layer-2 SAP encapsulation Yes Yes Yes Yes Yes Yes Yes Yes

[1] Globally-configured QoS supports IPv6 packets starting in release K.14.01.

All switches

For explicit QoS support of IP subnets, HP recommends forcing IP subnets onto separate VLANs and then configuring VLAN-based classifiers 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. A port can be an untagged member of only one VLAN of a given protocol type. Otherwise, the switch cannot determine which VLAN should receive untagged traffic.

Maximum global QoS remarking entries

The switches covered in this guide accept the maximum number of configured outbound 802.1p priority and DSCP entries shown in the following table.

Maximum number of QoS entries.

Switch Maximum QoS remarking Notes
3800 Switches
  • Each IP Device (IP address) QoS configuration uses two entries.

  • Each TCP/UDP Port QoS configuration uses two entries.

  • All other global QoS classifier configurations use one entry each.

Switch 8212zl Series 5400zl 250[a] configured entries
Series 5300yl

[a] Configuring IP Device (IP address) and TCP/UDP global QoS classifiers reduces this maximum. For more information, see the Notes column.

If the global QoS configurations on a switch exceed the maximum number of entries shown in Maximum number of QoS entries., the following error message is displayed:

Unable to add this QoS rule. Maximum number (

entry-#:) already reached.

Not supported

Use of an inbound 802.1p packet priority as a classifier 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 use this priority as a classifier for changing the outbound priority to 0.

Fragmented packets and TCP/UDP

QoS is not performed on fragmented packets under TCP/UDP.

Monitoring shared resources

The QoS feature shares internal switch resources with several other features. The switch provides ample resources for all features. However, if the internal resources become fully subscribed, additional QoS provisions cannot be configured until the necessary resources are released from other uses. For information on determining the current resource availability and usage, see the Management and Configuration Guide for your switch.