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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-07
Chapter 33 Configuring QoS
Understanding QoS
Classification Based on QoS ACLs
Packets can also be classified in input policy maps based on an ACL lookup. The ACL classification is
communicated to an output policy by assigning a QoS group or number in the input policy map. To
classify based on ACL lookup, you first create an IP or MAC ACL. Configure a class map and use the
match access-group
{
acl-number
|
acl name
} class-map configuration command, and attach the class
map to a policy map.
Note
You cannot configure
match access-group
for an output policy map.
You can use IP standard, IP extended, or Layer 2 MAC ACLs to define a group of packets with the same
characteristics (a class). You use the
access-list
global configuration command to configure IP ACLS to
classify IP traffic based on Layer 3 and Layer 4 parameters. You use the
mac access-list extended
global
configuration command to configure Layer 2 MAC ACLs to classify IP and non-IP traffic based on
Layer 2 parameters.
Note
You cannot match IP fragments against configured IP extended ACLs to enforce QoS. IP fragments are
sent as best-effort. IP fragments are denoted by fields in the IP header.
You can use only ACLs with a permit action in a
match access-group
command. ACLs with a deny
action are never matched in a
QoS policy.
Note
Only one access-group is supported per class for an input policy map.
Classification Based on QoS Groups
A QoS group is an internal label used by the switch to identify packets as a members of a specific class.
The label is not part of the packet header and is restricted to the switch that sets the label. QoS groups
provide a way to tag a packet for subsequent QoS action without explicitly marking (changing) the
packet. You can then communicate an ACL match from an input policy map to an output policy map.
A QoS group is identified at ingress and used at egress; it is assigned in an input policy to identify
packets in an output policy. See
Figure 33-3
. The QoS groups help aggregate different classes of input
traffic for a specific action in an output policy.
Best-effort data (bronze data)—other traffic, including all
noninteractive traffic, regardless of importance.
Default
0
0
0
Less than best-effort data—noncritical, bandwidth-intensive
data traffic given the least preference. This is the first traffic type
to be dropped.
Level 1
Level 2
Level 3
2
4
6
0
0
0
0
0
0
Table 33-1
Typical Traffic Classifications (continued)
Traffic Type
DSCP
per-hop
DSCP
(decimal)
IP
Precedence
CoS
Summary of Contents for ME 3400 Series
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