Configuration > Quality of Service
Quality of Service (QoS) prioritizes network traffic and manages available bandwidth so that the most important traffic goes first. QoS is implemented as rules or policies that prioritize packets, optionally change information in the packet header, and assign them to outbound port queues based on their priority.
Each switch port has four types of outbound traffic queues based on priority: low, normal, medium, and high. The queue priority determines the order of exit for packets in the queue. For example, packets in a high priority queue leave the switch before packets in other queues.
To summarize:
QoS assigns a priority to each packet based on the classifier contained in its header and QoS settings in your switch.
Depending on QoS settings and if the packet leaves the switch through a port that is a tagged member of the VLAN, QoS optionally adds or changes information in the packet header.
Using the priority that QoS assigned to the packet, QoS selects an outbound port queue with the same priority level, as shown in the following table:
QoS Priority Assigned to Packet |
Port Queue |
Priority |
Order of Exit |
|
6-7 |
6-7 |
High |
1 |
|
4-5 |
4-5 |
Medium |
2 |
|
0, 3 |
0, 3 |
Normal |
3 |
|
1-2 |
1-2 |
Low |
4 |
Packets leave the switch based on the queue's order of priority.
For additional information, see Quality of Service Terms, Quality of Service Operating Notes, and Quality of Service in Tagged and Untagged VLANs.
Perform the following steps before configuring QoS for outbound traffic:
Determine the QoS policy you want to implement. This includes analyzing the types of traffic flowing through your network and identifying one or more traffic types to prioritize.
Determine the QoS type of service (IP Precedence or Differential Services) you want to use to prioritize outbound traffic.
If you want 802.1p priority settings to be included in outbound packets, ensure that tagged VLANs are configured on the appropriate links.
Use tagged VLANs to carry packet priority as an 802.1p value to downstream devices.
Determine the actual QoS configuration changes needed on each QoS-capable device in your network in order to implement the desired policy. Also, if you want downstream devices to read and use DSCP classifiers in IP packets from the switch, configure them to do so by enabling ToS Differentiated Service mode and making sure the same DSCP policies are configured.
If you use an HP network management tool (for example, ProCurve Manager) to configure QoS policy in a network, it overrides any QoS settings configured through the CLI or the Web Agent for ProCurve switches.
You configure QoS by defining QoS classifiers (information contained in incoming packet headers) and assigning a 802.1p priority (1-7) or DSCP policy (codepoint and 802.1p priority) to the classifier you want to use to prioritize packets. This priority determines the queue to which packets with the classifier are sent and whether packet header information is changed before sending it to downstream devices.
We recommend that you configure a minimum number of QoS classifiers, because increasing the number of active classifiers for a packet type increases the complexity of the possible outcomes.
Beginning with software release E.08.xx, the switch allows up to 400 802.1p priority rules and/or DSCP policies in any combination. See QoS Operating Notes for additional information.
The priority for a packet containing more than one QoS classifier is determined by the classifier that has the highest precedence as shown below. For example, a packet containing a defined IP address (precedence 2) and a defined DSCP (precedence 3) will be prioritized by the IP address and leave the switch before packets in lower priority queues (precedences 3-7).
Policy |
Classifier |
Precedence |
Description |
|
Virtual Port Number for Application |
1 |
Inbound IPv4 packets carrying the specified UDP/TCP port number are prioritized based on the priority level configured for the application type, which is determined by the 802.1p priority or DSCP policy you assign to the port number. Virtual port numbers are predefined for registered and well-known application types. In addition, you can create dynamic and private virtual port numbers for use exclusively within your network. | |
|
IP Address of Source or Destination Port |
2 |
Inbound packets carrying the specified source or destination IP address are prioritized based on the 802.1p priority (0-7) or DSCP (codepoint) you assign to the IP address. If a given packet has a destination IP address matching a QoS configuration, this packet takes precedence over another packet that has an IP address matching the source address. (This can occur, for example, on an outbound port in a switch mesh environment.) Also, if the source and destination IP addresses (SA and DA) in the same packet match for different QoS policies, the DA takes precedence. Default state: No IP address prioritization. If you prioritize the packet based on 802.1p priority, you can assign a new 802.p1 priority to the packet that will be sent to downstream devices. If you prioritize the packet based on DSCP (codepoint), you can assign a new codepoint to the packet in addition to a new 802.1p priority. See DSCP Policy Table for additional information.
| |
|
Type of Service (ToS) |
IP Precedence or DSCP |
3 |
Inbound packets are prioritized based on the IP precedence bits or DSCP (codepoint) contained in the ToS byte of their header. If you prioritize the packet based on IP precedence, you can assign a new 802.1p priority to the packet that will be sent to downstream devices. If you prioritize the packet based on DSCP (codepoint), you can assign a new codepoint to the packet in addition to a new 802.1p priority. See DSCP Policy Table for additional information. |
|
Quality of Service Protocol |
4 (Not available on all switches) |
Inbound packets are prioritized based on their protocol (IP, IPX, ARP, DEC LAT, Appletalk, SNA, or Netbeui). A protocol is assigned an 802.1p priority (0-7) that prioritizes the packet and is carried in the packet to downstream devices.
| |
|
VLAN ID |
5 (not available on all switches) |
Inbound packets are prioritized based on the VLAN ID (VID) contained in the header.
| |
|
Source Port |
Port that received packet |
6 (not available on all switches) |
Inbound packets are prioritized based on the port used by the packet to enter the switch.
|
|
Incoming 802.1 Priority (DSCP) |
802.1p priority |
7 |
When a VLAN-tagged packet enters the switch through a port that is a tagged member of that VLAN and QoS is not configured to override the packet’s 802.1p priority setting, the switch uses the packet’s existing 802.1p priority (assigned by a Priority upstream device or application) to determine which outbound port queue to use. If there is no QoS policy match on the packet and it leaves the switch through a port that is a tagged member of the VLAN, its 802.1p priority setting is not changed. If the packet leaves the switch through a port that is an untagged member of the VLAN, the 802.1p priority is dropped. |
The type of switch determines the precedence search order. Precedence 1 is the highest precedence for all switches except:
Precedence 1 - Low
2600 (1-6)
2610 (1-5)
2800 (1-6)
If only one configured classifier matches a given packet, the switch applies the QoS policy specified in that classifier. If multiple configured classifiers match a given packet, the switch applies each one in turn to the packet and concludes with the QoS policy for the highest precedence classifier. Note that if the highest precedence classifier is configured to apply a DSCP policy, then both the DSCP in the packet and the 802.1p priority applied to the packet can be changed. However, if the highest precedence classifier is configured to apply an 802.1p priority rule, only the 802.1p priority in the final QoS match for the packet is changed. For additional information, refer to the Advanced Traffic Management Guide for your switch.
If a packet does not meet the criteria for Incoming 802.1p priority, the packet goes to the normal outbound queue of the appropriate port. If the packet enters the switch on an untagged VLAN, but exits on a tagged VLAN, an Incoming tagged VLAN field, including an 802.1p priority of 0 (normal), is added to the packet.
By default, the ToS, Protocol, and VLAN priorities automatically list each of their priority options as No-override. (Some ToS codepoints use default priority settings defined by the DSCP standard.) This means that if you do not configure a specific priority, QoS does not prioritize packets to which that priority applies. For example, if you do not specify a priority for the IP protocol, then the IP protocol will not be a criteria for setting a QoS priority and the packets will be handled as described above.
The Quality of Service window can be used to enable the IP Precedence or Differential Services type of service. This window is also used to define the DSCP Policy Table and Class of Service for Differential Services, as explained in Differential Services.
Enabling IP Precedence or Differential Services automatically disables the other.
IP Precedence simply reads the classifier contained in the packet header and sends the packet to the associated port queue.
Differential Services uses the classifier contained in the packet header to select the associated DSCP policy defined in the switch. This DSCP policy establishes the priority used to assign the packet to an outbound port queue and, optionally, changes the classifier in the packet header.
Regardless of the type of service used, if the packet leaves the switch through a port that is a tagged member of the VLAN, the priority setting is carried to the destination switch. If the packet leaves the switch through a port that is an untagged member of the VLAN, the 802.1p priority is dropped.
Additional types of service can be enabled through the CLI. For additional information, see the Advanced Traffic Management Guide for your switch.