Mapping Tables - Cisco Catalyst 2950 Software Manual

Chapter 13 Configuring QoS
For IP traffic, you have these classification options:
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When configuring policing and policers, keep these items in mind:
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No policers can be configured on the egress interface on Catalyst 2950 switches.
Note

Mapping Tables

This feature is available only if your switch is running the enhanced software image.
Note
The Catalyst 2950 switches support these types of marking to apply to the switch:
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An interface can be configured to trust either CoS or DSCP, but not both at the same time.
Note
Before the traffic reaches the scheduling stage, QoS uses the configurable DSCP-to-CoS map to derive
a CoS value from the internal DSCP value.
The CoS-to-DSCP and DSCP-to-CoS map have default values that might or might not be appropriate for
your network.
For configuration information, see the
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Trust the IP DSCP in the incoming packet (configure the port to trust DSCP), and assign the same DSCP
to the packet for internal use. The IETF defines the 6 most-significant bits of the 1-byte Type of
Service (ToS) field as the DSCP. The priority represented by a particular DSCP value is
configurable. The supported DSCP values are 0, 8, 10, 16, 18, 24, 26, 32, 34, 40, 46, 48, and 56.
Trust the CoS value (if present) in the incoming packet, and generate the DSCP by using the
CoS-to-DSCP map.
By default, no policers are configured.
Policers can only be configured on a physical port. There is no support for policing at a VLAN or
switched virtual interface (SVI) level.
Only one policer can be applied to a packet in the input direction.
Only the average rate and committed burst parameters are configurable.
Policing occurs on the ingress interfaces:
– 60 policers are supported on ingress Gigabit-capable Ethernet ports.
– 6 policers are supported on ingress 10/100 Ethernet ports.
– Granularity for the average burst rate is 1 Mbps for 10/100 ports and 8 Mbps for Gigabit
Ethernet ports.
On an interface configured for QoS, all traffic received through the interface is classified, policed,
and marked according to the policy map attached to the interface. On a trunk interface configured
for QoS, traffic in all VLANs received through the interface is classified, policed, and marked
according to the policy map attached to the interface.
CoS value to the DSCP value
DSCP value to CoS value
"Configuring CoS Maps" section on page
Catalyst 2950 Desktop Switch Software Configuration Guide
Understanding QoS
13-21.
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