7 Cisco
Configuration
There are basically two different classes of Cisco switch PSEs, fixed and chassis. A fixed switch has very
little hardware configuration ability if any after it is purchased. Fixed switches generally don’t have
redundant power supplies, few features and flexibility compared to chassis-based switches. Examples of
fixed switches include the Catalyst 3560 and 3750. These are relatively inexpensive switches used for
access to the network.
Chassis-based switches have a cabinet that houses cards or blades. These cards can be replaced with
other cards to meet the changing needs of a business such as migrating from copper ports to fiber ports.
Although more expensive, they offer more features, redundancy, and again, can be reconfigured to meet
business changes or growth. Examples of enterprise switches are the Catalyst 4500 and 6500 series.
Some chassis-based switches can operate with either one of two operating systems (OS) – Cat-OS and
IOS. Cisco is migrating from Cat-OS to IOS and over time will only support IOS. But many enterprises still
use Cat-OS and the command syntax is different than using IOS. This section does not list all possible
commands for one or both OS platforms – just the most important commands to control PoE.
Fixed Switch Configuration
Fixed switches like the Catalyst 3560 and 3750 have power sensing enabled on all ports by default. This
means all ports continually sense for a valid PD and if found, will provide power based on class for non-
Cisco PDs. The
show power inline
command will display the total amount of power, the power used
and power remaining for that switch.
There are three states under the Admin column, Auto, Never and Static. The syntax to apply one of these
commands is:
power inline
{
auto
[max
max-wattage
]|
never
|
static
[max
max-wattage
]}
Auto
is an automatic mode that senses the PoE class and then delivers the maximum power of that class’s
range if enough power is available. The example above displays 7.0 Watts for port fa/01 because it is a
class 2 PD. Port fa0/2 displays 15.4 Watts because the PD on that port is a class 3 device. When all
available power is allocated, no remaining ports can be powered.
Never
is used to disable power and power sensing on that port (interface). Non-PDs like desk-top PCs are
good candidates for this command.
Static
is used to pre-allocate power to a port even before the switch senses a valid PD. This is a priority
scheme to make sure the most important PDs always receive power.
MJK
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2006 Avaya Inc. All Rights Reserved.
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