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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Egress DSCP and CoS Sources
For the egress IP traffic, QoS creates a ToS byte from the internal DSCP value (which you can set equal
to an IP precedence value) and sends it to the egress port to be written into the IP packets. For the
trust-dscp
and
untrusted
IP traffic, the ToS byte includes the original 2 least-significant bits from the
received ToS byte.
For all egress traffic, QoS uses a configurable mapping table to derive a CoS value from the internal
DSCP value that is associated with the traffic (see the
“Mapping the Internal DSCP Values to the Egress
CoS Values” section on page 52-74
). QoS sends the CoS value to the Ethernet egress ports for use in
scheduling and to be written into the ISL and 802.1Q frames.
ACLs
QoS uses the ACLs that contain the ACEs. The ACEs specify the classification criteria, a marking rule,
and the policers. QoS compares the received traffic to the ACEs in the ACLs until a match occurs. When
the traffic matches the classification criteria in an ACE, QoS marks and polices the packet as specified
in the ACE and makes no further comparisons.
There are three ACL types: IP, and with a Layer 3 switching engine, IPX and MAC. QoS compares the
traffic of each type (IP, IPX, and MAC) only to the corresponding ACL type (see
Table 52-2
).
QoS supports the user-created
named
ACLs, each containing an ordered list of ACEs, and the
user-configurable
default
ACLs, each containing a single ACE.
Named ACLs
You create a named ACL when you enter an ACE with a new ACL name. You add an ACE to an existing
ACL when you enter an ACE with the name of the existing ACL.
You can specify the classification criteria for each ACE in a named ACL. The classification criteria can
be specific values or wildcards (for more information, see the
“Creating or Modifying ACLs” section on
page 52-45
).
Table 52-2
Supported EtherType Field Values
ACL Type
EtherType Field Value
Protocol
IP
0x0800
IP
IPX
1
1.
The PFC3 does not provide QoS for the IPX traffic.
0x8137 and 0x8138
IPX
MAC
2
2.
The QoS MAC ACLs that do not include an EtherType parameter match the traffic with any value in the EtherType field,
which allows MAC-level QoS to be applied to any traffic except IP and IPX.
0x0600 and 0x0601
XNS
0x0BAD and 0x0BAF
Banyan VINES
0x6000-0x6009 and 0x8038-0x8042
DECnet
0x809b and 0x80f3
AppleTalk