that has 802.1Q tagging turned on.
For diffserv, each of the diffserv code points (DSCP) can have a priority set for it. It is
also possible to set a new DSCP and 802.1p priority based on the incoming DSCP, or set
the 802.1p priority alone based on the incoming DSCP. The ability to re-write the DSCP
allows the network manager to:
Identify packets coming from a different area of the network, such as a remote site,
Redefine an incoming DSCP to conform to the DSCP definitions defined in the local
Protocol Priority (IP, IPX, ARP, DEC LAT, AppleTalk, SNA, and NetBEUI)
VLAN ID: Allows a VLAN to be assigned a specific priority. Can also remap the DSCP.
Incoming source-port on the switch. Can also remap the DSCP.
Incoming 802.1p Priority (present in tagged VLAN environments)
If the DSCP is remapped, the 802.1p priority associated with the new DSCP is used to determine the
priority queue on the outbound port. In addition, these 802.1p bits will be included in the outgoing
packet if VLAN tagging is specified for the outbound port.
2.4.3 IEEE 802.1p Priority Support
IEEE 802.1Q packet tagging supports both designation of VLAN membership (see the VLAN section
below) and packet priority (up to 8 levels and often referred to as 802.1p). Since 802.1p has 8 levels of
priority possible, but the switch has only 4 physical priority levels, the following mappings are used:
Packets without any 802.1p tagging are assigned by the switch internally to 802.1p priority 0. This is
mapped to the normal queue in the switch so that untagged packets are not penalized in priority. These
priority queue mappings are set as designated in the 802.1Q standard.
2.4.4 Diffserv / TOS Support
As mentioned in the Classifiers section above, the HP ProCurve Switch 5300xl Series provide very
flexible control of the diffserv (DSCP) bits. Mapping of each of the 64 possible DSCPs can specify an
802.1p priority, as well as a new DSCP for the outbound packet.
Diffserv code points are in their early acceptance for use in networks. Their importance will grow as
more networks and applications take advantage of them.
Since TOS IP Precedence and DSCP are mutually exclusive (they use the same set of bits in the IP
header), the switch will allow only TOS IP Precedence definitions or only DSCP definitions to be active
at any one time.
Some other switch vendors use non-standard priority mappings in their switches.
© Hewlett-Packard Co. 2002, 2003
HP ProCurve Switch 5300xl Series Reviewer's Guide
by changing the DSCP as it comes through the HP ProCurve Switch 5300xl
Series and treating this remote packet differently than packets originating in the
Switch priority queue
Rev 1.1 – 2/11/2003
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