3400Cl/6400Cl Packet Classifiers And Evaluation Order - HP ProCurve 5300xl Series Management Manual

Quality of Service (QoS): Managing Bandwidth More Effectively
Introduction
N o t e
8-10

3400cl/6400cl Packet Classifiers and Evaluation Order

The 3400cl/6400cl switches provide six QoS classifiers (packet criteria) you
can use to configure QoS priority.
Table 8-5. 3400cl/6400cl Classifier Search Order and Precedence
Search Order Precedence QoS Classifier
1 6 (lowest)
2 5
3 4
4 3
5 2
6 1 (highest)
A 3400cl or 6400cl switch uses the lowest-to-highest search order shown in
table 8-5 to identify the highest-precedence classifier to apply to any given
packet. (Note that this is the opposite of the order used in the 5300xl switches.)
If there is only one configured classifier that matches a given packet, then 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 classi­
fier. 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.
On the 3400cl/6400cl switches, intermixing lower-precedence classifiers con-
figured with DSCP policies and higher-precedence classifiers configured with
802.1p priority rules is not recommended, as this can result in a packet with
an 802.1p priority assigned by one classifier and a DSCP policy by another
classifier. This is because the search order would allow a lower precedence
classifier configured with a DSCP policy to change both the DSCP and the
802.1p setting in a packet, and then would allow a subsequent, higher prece­
dence classifier configured with an 802.1p priority rule to change only the
802.1p setting. To avoid this problem, a DSCP policy option should be applied
only on the highest-precedence classifier in use on the switch or applied to
all QoS classifiers in use on the switch.
Incoming 802.1p Priority (present in tagged VLAN environments)
Incoming source-port on the switch
VLAN Priority
IP Type of Service (ToS) field (IP packets only)
Device Priority (destination or source IP address)
UDP/TCP Application Type (port)