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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 10 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Cisco IP Phones and access points can also be connected to an AC power source and supply their own
power.
For information about configuring a switch port to forward IP voice traffic to and from connected
Cisco IP Phones, see the
“Configuring a Port to Connect to a Cisco 7960 IP Phone” section on page 14-3
Beginning in privileged EXEC mode, follow these steps to enable the inline-power on an inline-power
capable port:
To permanently disable inline-power on a port, use the power inline never interface configuration
command.
Configuring IEEE 802.3X Flow Control
Flow control enables connected Ethernet ports to control traffic rates during congestion by allowing
congested nodes to pause link operation at the other end. If one port experiences congestion and cannot
receive any more traffic, it notifies the other port to stop sending until the condition clears. When the
local device detects any congestion at its end, it can notify the link partner or the remote device of the
congestion by sending a pause frame. Upon receipt of a pause frame, the remote device stops sending
any data packets, which prevents any loss of data packets during the congestion period.
Note
You must not configure both IEEE 802.3X flowcontrol and quality of service (QoS) on a switch. Before
configuring flowcontrol on an interface, use the no mls qos global configuration command to disable
QoS on the switch.
Flow control can be implemented in two forms, symmetric and asymmetric. The symmetric
implementation is suitable for point-to-point links, and asymmetric is suitable for hub-to-end node
connections, where it is desirable for the hub to pause the end system, but not vice-versa. You use the
flowcontrol interface configuration command to set the interface’s ability to receive and send pause
frames to on, off, or desired. The default state for Gigabit Ethernet ports is receive off and send desired.
The default state for Fast Ethernet ports is receive off and send off.
Note
On Catalyst 3550 switches, Gigabit Ethernet ports are capable of receiving and sending pause frames;
Fast Ethernet ports can only receive pause frames. Therefore, for Fast Ethernet ports, only the conditions
described with send off are applicable.
These rules apply to flow control settings on the device:
•
receive on (or desired) and send on: Flow control operates in both directions; both the local and the
remote devices can send pause frames to show link congestion.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface interface
Enter interface configuration mode, and enter the port to be configured.
Step 3
power inline auto
Automatically detect and enable inline power on the port. This is the default.
Step 4
end
Return to privileged EXEC mode.
Step 5
show power inline interface
Verify the change.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.