Configuration Guide (Supporting R05.6.00) Manual

Multi-Service IronWare QoS and Traffic Management Configuration Guide 43
53-1003037-02
Ingress Traffic processing through a device
3
3. Force the priority and drop precedence value based on the value configured for the physical
port.
4. Force the priority value based on an ACL look-up. This is used for setting a a specific priority for
and L2, L3 or L4 traffic flow.
NOTE
DEI value will remain 0 regardless of PCP or DSCP value.
Recognizing inbound packet priorities and mapping
to internal priority
Stage 1
Collect priority and drop precedence information from various portions of the
packet header
• If a packet’s EtherType matches 8100 or the port’s EtherType, derive a priority value and drop
precedence by decoding the PCP value.
• For IPv4 packets, derive a priority value and drop precedence by decoding the DSCP bits.
• The derived values for PCP, and DSCP are mapped to a default map.
• To assist the device in the decoding process described in “stage 1” decode-map tables are
defined.
Stage 2
Determine if a priority value should be forced
• If a packet’s EtherType matches 8100 or the port’s EtherType, derive a priority value and drop
precedence by decoding the PCP value
• If the qos pcp force command is configured on the port, the priority and drop precedence
values are set to the value read from the PCP bits.
• If the qos dscp force command is configured on the port, the priority and drop precedence
values are set to the value read from the DSCP bits.
• If none of the qos force commands are configured, the priority and drop precedence values of
a given packet is obtained in the following manner:
• For Tagged and Untagged IPv4Packets: Priority and drop precedence values obtained from
decoded DSCP values.
• For Tagged Non-IPv4 Packets: Priority and drop precedence values obtained from decoded
PCP values.
• For Untagged, Non-IPv4 Packets: Priority and drop precedence values obtained from
priority and drop precedence assigned on a port. If no priority and drop precedence is
assigned on a port default value of Priority 0 and Drop Precedence 0 is picked.