52-15
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Ethernet Ingress Port Classification Features with a Layer 3 Switching Engine
You can use the
untrusted
,
trust-ipprec
,
trust-dscp
, and
trust-cos
port keywords to classify the traffic
on a per-port basis for a Layer 3 switching engine to mark.
The
trust-ipprec
and
trust-dscp
keywords are supported only with a Layer 3 switching engine and are
not supported on the
1q4t
ports except Gigabit Ethernet. On the
1q4t
ports (except Gigabit Ethernet),
the
trust-cos
port keyword displays an error message, activates the receive-queue drop thresholds,
and—as indicated by the error message—does not apply the
trust-cos
trust state to the traffic. You must
configure the
trust-cos
ACL that matches the ingress traffic to apply the
trust-cos
trust state.
In addition to the per-port classification, you can create the ACEs that classify the traffic on a per-packet
basis (for the IP and IPX traffic, see the
“Named IP ACLs” section on page 52-46
and the
“Creating or
Modifying the Named IPX ACLs” section on page 52-51
) or on a per-frame basis (for the other traffic,
see the
“Creating or Modifying the Named MAC ACLs” section on page 52-53
), regardless of the port
configuration (see the
“Marking Rules” section on page 52-23
).
To mark the traffic in response to per-port classification, the traffic must match an ACE that contains the
dscp
ACE keyword (see the
“Marking Rules” section on page 52-23
). In their default configuration, the
ACEs in the default ACLs contain the
dscp
ACE keyword.
Table 52-1
lists the per-port classifications
and the marking rules that they invoke.
QoS uses the configurable mapping tables to set the internal and egress DSCP, which is a 6-bit value,
from the CoS and IP precedence, which are 3-bit values (for more information, see the
“Internal DSCP
Values” section on page 52-16
and the
“Configuring the DSCP Value Maps” section on page 52-73
).
Classification, Marking, and Policing with a Layer 3 Switching Engine
Note
With a Layer 3 switching engine, the Catalyst 6500 series switches provide QoS only for the following
frame types: Ethernet_II, Ethernet_802.3, Ethernet_802.2, and Ethernet_SNAP.
Table 52-1
Marking Based on Per-Port Classification
Port Keyword ACE Keyword Marking Rule
untrusted dscp
Set the internal and egress DSCP as specified in the ACE.
trust-ipprec dscp
For the IP traffic, set the internal and egress DSCP from the received Layer 3 IP precedence
value. For the other traffic, set the internal and egress DSCP from the received or port Layer 2
CoS value.
Note
—With the
trust-ipprec
port keyword, QoS uses only the IP precedence bits. If the traffic
with a DSCP value enters the switch through a port that is 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 the IP traffic, set the internal and egress DSCP from the received Layer 3 DSCP value. For
other traffic, set the internal and egress DSCP from the received or port Layer 2 CoS value.
trust-cos dscp
Set the internal and egress DSCP from the received or port Layer 2 CoS value.
