41-14
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
78-13315-02
Chapter 41 Configuring QoS
Understanding How QoS Works
QoS uses configurable mapping tables to set internal and egress DSCP, which is a 6-bit value, from CoS
and IP precedence, which are 3-bit values (for more information, see the
“Internal DSCP Values” section
on page 41-15
and the
“Configuring DSCP Value Maps” section on page 41-55
).
Classification, Marking, and Policing with a Layer 3 Switching Engine
Note
With a Layer 3 switching engine, the Catalyst 6000 family switches provide QoS only for the
following frame types: Ethernet_II, Ethernet_802.3, Ethernet_802.2, and Ethernet_SNAP.
These sections describe classification, marking, and policing with a Layer 3 switching engine:
•
Internal DSCP Values, page 41-15
•
ACLs, page 41-15
•
Named ACLs, page 41-16
•
Default ACLs, page 41-20
•
Marking Rules, page 41-21
•
Policing Rules, page 41-22
•
PFC2 Policing Decisions, page 41-23
•
Attaching ACLs, page 41-23
•
Final Layer 3 Switching Engine CoS and ToS Values, page 41-24
Note
Classification with a Layer 3 switching engine uses Layer 2, 3, and 4 values. Marking with a Layer 3
switching engine uses Layer 2 CoS values and Layer 3 IP precedence or DSCP values.
Table 41-1
Marking Based on Per-Port Classification
Port Keyword ACE Keyword Marking Rule
untrusted dscp
Set internal and egress DSCP as specified in the ACE.
trust-ipprec dscp
For IP traffic, set internal and egress DSCP from the received Layer 3
IP precedence value. For other traffic, set internal and egress from the
received or port Layer 2 CoS value.
Note
—With the
trust-ipprec
port keyword, QoS uses only the IP
precedence bits. If traffic with a DSCP value enters the switch through
a port configured with the
trust-ipprec
port keyword, the three most
significant bits of the DSCP value are interpreted as an IP precedence
value; QoS ignores the rest of the DSCP value.
trust-dscp dscp
For IP traffic, set internal and egress DSCP from the received Layer 3
DSCP value. For other traffic, set internal and egress DSCP from the
received or port Layer 2 CoS value.
trust-cos dscp
Set internal and egress DSCP from the received or port Layer 2 CoS
value.
