Enabling Pass-Through Mode - Cisco Catalyst 2950 Software Configuration Manual

Chapter 29 Configuring QoS
Table 29-6
Table 29-6
Port Configuration
The port trusts the CoS value
of the incoming packet.
The port trusts the DSCP
value of the incoming packet.
The port assigns the default
CoS value to incoming
packets.

Enabling Pass-Through Mode

In software releases earlier than Cisco IOS Release 12.1(11)EA1, the switch is in pass-through mode. It
uses the CoS value of incoming packets without modifying the DSCP value and sends the packets from
one of the four egress queues. You cannot enable or disable pass-through mode if your switch is running
a software release earlier than Cisco IOS Release 12.1(11)EA1.
In Cisco IOS Release 12.1(11)EA1 or later, the switch assigns a CoS value of 0 to all incoming packets
without modifying the packets. The switch offers best-effort service to each packet regardless of the
packet contents or size and sends it from a single egress queue.
Beginning in privileged EXEC mode, follow these steps to enable pass-through mode:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3 mls qos trust cos pass-through dscp Enable pass-through mode. The interface is configured to trust the CoS
Step 4 end
Step 5 show mls qos interface [interface-id] Verify your entries.
Step 6
copy running-config startup-config
To disable pass-through mode, use the no mls qos trust pass-through dscp interface configuration
command.
If you enter the mls qos cos override and the mls qos trust [cos | dscp] interface commands when
pass-through mode is enabled, pass-through mode is disabled.
78-11380-12
lists the port configuration when an IP phone is present or absent.
Port Configurations When Trusted Boundary is Enabled
When a Cisco IP Phone is Present
The packet CoS value is trusted.
The packet DSCP value is trusted. For tagged non-IP packets, the
The packet CoS value is assigned
the default CoS value.
Purpose
Enter global configuration mode.
Specify the interface on which pass-through mode is enabled, and enter
interface configuration mode.
Valid interfaces include physical interfaces.
value of the incoming packets and to send them without modifying the
DSCP value.
Return to privileged EXEC mode.
(Optional) Save your entries in the configuration file.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
Configuring Standard QoS
When a Cisco IP Phone is Absent
The packet CoS value is assigned
the default CoS value.
packet CoS value is set to 0.
For untagged non-IP packets, the
packet CoS value is assigned the
default CoS value.
The packet CoS value is assigned
the default CoS value.
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